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Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2017	Feb. 28, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Entity Registrant Name	MIDDLESEX WATER CO
Entity Central Index Key	0000066004
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity a Well-known Seasoned Issuer	No
Entity a Voluntary Filer	No
Entity Reporting Status Current	Yes
Entity Filer Category	Accelerated Filer
Entity Public Float			$ 624,441,708
Entity Common Stock, Shares Outstanding		16,351,940
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2017

CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	12 Months Ended
CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Operating Revenues	$ 130,775	$ 132,906	$ 126,025
Operating Expenses:
Operations and Maintenance	64,668	65,534	65,167
Depreciation	13,922	12,796	12,051
Other Taxes	13,565	13,944	12,967
Total Operating Expenses	92,155	92,274	90,185
Operating Income	38,620	40,632	35,840
Other Income (Expense):
Allowance for Funds Used During Construction	702	619	380
Other Income	123	662	208
Other Expense	(30)	(2,143)	(295)
Total Other Income (Expense), net	795	(862)	293
Interest Charges	5,506	5,293	5,554
Income before Income Taxes	33,909	34,477	30,579
Income Taxes	11,100	11,735	10,551
Net Income	22,809	22,742	20,028
Preferred Stock Dividend Requirements	144	144	144
Earnings Applicable to Common Stock	$ 22,665	$ 22,598	$ 19,884
Earnings per share of Common Stock:
Basic	$ 1.39	$ 1.39	$ 1.23
Diluted	$ 1.38	$ 1.38	$ 1.22
Average Number of Common Shares Outstanding :
Basic	16,330,000	16,270,000	16,175,000
Diluted	16,486,000	16,426,000	16,331,000
Cash Dividends Paid per Common Share	$ 0.858	$ 0.808	$ 0.776

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
UTILITY PLANT:
Water Production	$ 153,844	$ 146,914
Transmission and Distribution	468,649	430,880
General	69,457	63,514
Construction Work in Progress	11,562	12,196
TOTAL	703,512	653,504
Less Accumulated Depreciation	146,272	135,728
UTILITY PLANT - NET	557,240	517,776
CURRENT ASSETS:
Cash and Cash Equivalents	4,937	3,879
Accounts Receivable, net	10,785	10,129
Unbilled Revenues	6,999	6,590
Materials and Supplies (at average cost)	4,118	4,094
Prepayments	2,408	2,024
TOTAL CURRENT ASSETS	29,247	26,716
Preliminary Survey and Investigation Charges	4,676	2,365
Regulatory Assets	58,423	60,894
Operations Contracts, Developer and Other Receivables	439	1,139
Restricted Cash	1,460	439
Non-utility Assets - Net	9,478	9,131
Federal Income Tax Receivable		1,408
Other	177	293
TOTAL DEFERRED CHARGES AND OTHER ASSETS	74,653	75,669
TOTAL ASSETS	661,140	620,161
CAPITALIZATION:
Common Stock, No Par Value	155,120	153,045
Retained Earnings	74,055	65,392
TOTAL COMMON EQUITY	229,175	218,437
Preferred Stock	2,433	2,436
Long-term Debt	139,045	134,538
TOTAL CAPITALIZATION	370,653	355,411
CURRENT LIABILITIES:
Current Portion of Long-term Debt	6,865	6,159
Notes Payable	28,000	12,000
Accounts Payable	13,929	12,343
Accrued Taxes	11,418	12,385
Accrued Interest	1,093	1,084
Unearned Revenues and Advanced Service Fees	951	923
Other	2,281	2,162
TOTAL CURRENT LIABILITIES	64,537	47,056
DEFERRED CREDITS AND OTHER LIABILITIES:
Customer Advances for Construction	21,423	20,846
Accumulated Deferred Income Taxes	43,160	72,825
Employee Benefit Plans	36,686	36,139
Regulatory Liabilities	43,745	11,337
Other	1,315	1,443
TOTAL DEFERRED CREDITS AND OTHER LIABILITIES	146,329	142,590
CONTRIBUTIONS IN AID OF CONSTRUCTION	79,621	75,104
TOTAL CAPITALIZATION AND LIABILITIES	$ 661,140	$ 620,161

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CASH FLOWS FROM OPERATING ACTIVITIES:
Net Income	$ 22,809	$ 22,742	$ 20,028
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:
Depreciation and Amortization	14,846	13,532	13,087
Provision for Deferred Income Taxes	7,944	3,553	15,753
Equity Portion of Allowance For Funds Used During Construction (AFUDC)	(481)	(423)	(228)
Cash Surrender Value of Life Insurance	(209)	(101)	(76)
Stock Compensation Expense	840	829	633
Adoption of Repairs on Tangible Property Regulations Net			2,680
Changes in Assets and Liabilities:
Accounts Receivable	(656)	(69)	(48)
Unbilled Revenues	(409)	(344)	(309)
Materials & Supplies	(24)	(1,494)	(347)
Prepayments	(384)	11	(46)
Accounts Payable	1,586	5,818	171
Accrued Taxes	(967)	3,259	178
Accrued Interest	9	(20)	(30)
Employee Benefit Plans	(1,920)	(1,601)	(129)
Unearned Revenue & Advanced Service Fees	28	43	41
Other Assets and Liabilities	(169)	1,336	(146)
NET CASH PROVIDED BY OPERATING ACTIVITIES	42,843	47,071	51,212
CASH FLOWS FROM INVESTING ACTIVITIES:
Utility Plant Expenditures, Including AFUDC of $221 in 2017, $196 in 2016 and $152 in 2015	(50,301)	(47,375)	(25,773)
(Receipt) Release of Restricted Cash	(1,021)		1,390
NET CASH USED IN INVESTING ACTIVITIES	(51,322)	(47,375)	(24,383)
CASH FLOWS FROM FINANCING ACTIVITIES:
Redemption of Long-term Debt	(6,159)	(5,898)	(6,284)
Proceeds from Issuance of Long-term Debt	11,523	8,585	7,000
Net Short-term Bank Borrowings	16,000	9,000	(16,000)
Deferred Debt Issuance Expense	(230)	(152)	(65)
Common Stock Issuance Expense			(22)
Restricted Cash			744
Proceeds from Issuance of Common Stock	1,234	1,453	1,462
Payment of Common Dividends	(14,002)	(13,137)	(12,553)
Payment of Preferred Dividends	(144)	(144)	(144)
Construction Advances and Contributions-Net	1,315	1,007	(171)
NET CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES	9,537	714	(26,033)
NET CHANGES IN CASH AND CASH EQUIVALENTS	1,058	410	796
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	3,879	3,469	2,673
CASH AND CASH EQUIVALENTS AT END OF PERIOD	4,937	3,879	3,469
SUPPLEMENTAL DISCLOSURE OF NON-CASH ACTIVITY:
Utility Plant received as Construction Advances and Contributions	3,778	1,439	2,441
Long-term Debt Deobligation		476	466
Cash Paid During the Year for:
Interest	5,616	5,430	5,702
Interest Capitalized	221	196	152
Income Taxes	$ 2,754	$ 5,729	$ 1,391

CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Cash Flows [Abstract]
Allowance for funds used during construction	$ 221	$ 196	$ 152

CONSOLIDATED STATEMENTS OF CAPITAL STOCK AND LONG-TERM DEBT - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Common Stock, No Par Value	$ 155,120	$ 153,045
Retained Earnings	74,055	65,392
TOTAL COMMON EQUITY	229,175	218,437
TOTAL PREFERRED STOCK	2,433	2,436
SUBTOTAL LONG-TERM DEBT	147,852	142,489
Add: Premium on Issuance of Long-term Debt	1,367	1,495
Less: Unamortized Debt Expense	(3,309)	(3,287)
Less: Current Portion of Long-term Debt	(6,865)	(6,159)
TOTAL LONG-TERM DEBT	139,045	134,538
Convertible Preferred Stock $7.00 Series
SUBTOTAL LONG-TERM DEBT	1,005	1,007
Convertible Preferred Stock $8.00 Series [Member]
SUBTOTAL LONG-TERM DEBT	349	349
Nonredeemable Preferred Stock $7.00 Series
SUBTOTAL LONG-TERM DEBT	79	80
Nonredeemable Preferred Stock $4.75 Series [Member]
SUBTOTAL LONG-TERM DEBT	1,000	1,000
Amortizing Secured Note, due December 20, 2021 [Member]
SUBTOTAL LONG-TERM DEBT	1,180	1,415
Amortizing Secured Note, due May 19, 2028 [Member]
SUBTOTAL LONG-TERM DEBT	4,375	4,795
Amortizing Secured Note, due August 25, 2030 [Member]
SUBTOTAL LONG-TERM DEBT	3,547	3,827
Amortizing Secured Note, due September 19, 2031 [Member]
SUBTOTAL LONG-TERM DEBT	3,827	4,107
State Revolving Trust Note, due December 31, 2022 [Member]
SUBTOTAL LONG-TERM DEBT	279	329
State Revolving Trust Note, due May 1, 2025 [Member]
SUBTOTAL LONG-TERM DEBT	1,851	2,062
State Revolving Trust Note, due March 1, 2026 [Member]
SUBTOTAL LONG-TERM DEBT	392	431
State Revolving Trust Note2 [Member]
SUBTOTAL LONG-TERM DEBT	427	465
State Revolving Trust Note, due December 1, 2026 [Member]
SUBTOTAL LONG-TERM DEBT	553	603
State Revolving Trust Bond 4.00% to 5.00%, due August 1, 2021 [Member]
SUBTOTAL LONG-TERM DEBT	162	213
State Revolving Trust Bond 0.00%, due August 1, 2021 [Member]
SUBTOTAL LONG-TERM DEBT	128	166
State Revolving Trust Note, due July 1, 2028 [Member]
SUBTOTAL LONG-TERM DEBT	256	276
State Revolving Trust Note, due January 1, 2028 [Member]
SUBTOTAL LONG-TERM DEBT	84	91
State Revolving Trust Note, due August 1, 2031 [Member]
SUBTOTAL LONG-TERM DEBT	962	1,015
Amortizing Secured Note, due April 20, 2029 [Member]
SUBTOTAL LONG-TERM DEBT	3,953	4,302
Amortizing Secured Note 7.05%, due January 20, 2030 [Member]
SUBTOTAL LONG-TERM DEBT	3,021	3,271
Amortizing Secured Note 5.69%, due January 20, 2030 [Member]
SUBTOTAL LONG-TERM DEBT	6,197	6,709
4.45%, Amortizing Secured Note, due April 20, 2040 [Member]
SUBTOTAL LONG-TERM DEBT	9,827	10,267
4.47%, Amortizing Secured Note, due April 20, 2040 [Member]
SUBTOTAL LONG-TERM DEBT	3,646	3,810
State Revolving Trust Note, due July 1, 2031 [Member]
SUBTOTAL LONG-TERM DEBT	2,075	2,191
State Revolving Trust Note, due February 1, 2036 [Member]
SUBTOTAL LONG-TERM DEBT	1,115	1,115
State Revolving Trust Note, due November 30, 2030 [Member]
SUBTOTAL LONG-TERM DEBT	1,090	1,154
Construction Loans [Member]
SUBTOTAL LONG-TERM DEBT	3,874	7,470
First Mortgage Bonds - Series X [Member]
SUBTOTAL LONG-TERM DEBT	55	107
First Mortgage Bonds - Series Y [Member]
SUBTOTAL LONG-TERM DEBT	61	122
First Mortgage Bonds - Series Z [Member]
SUBTOTAL LONG-TERM DEBT	224	335
First Mortgage Bonds - Series AA [Member]
SUBTOTAL LONG-TERM DEBT	300	440
First Mortgage Bonds - Series BB [Member]
SUBTOTAL LONG-TERM DEBT	482	603
First Mortgage Bonds - Series CC [Member]
SUBTOTAL LONG-TERM DEBT	636	779
First Mortgage Bonds - Series EE [Member]
SUBTOTAL LONG-TERM DEBT	2,296	2,713
First Mortgage Bonds - Series FF [Member]
SUBTOTAL LONG-TERM DEBT	3,495	3,690
First Mortgage Bonds - Series GG [Member]
SUBTOTAL LONG-TERM DEBT	813	903
First Mortgage Bonds - Series HH [Member]
SUBTOTAL LONG-TERM DEBT	880	960
First Mortgage Bonds - Series II [Member]
SUBTOTAL LONG-TERM DEBT	610	700
First Mortgage Bonds - Series JJ [Member]
SUBTOTAL LONG-TERM DEBT	750	824
First Mortgage Bonds - Series KK [Member]
SUBTOTAL LONG-TERM DEBT	988	1,078
First Mortgage Bonds - Series LL [Member]
SUBTOTAL LONG-TERM DEBT	1,095	1,175
First Mortgage Bonds - Series MM [Member]
SUBTOTAL LONG-TERM DEBT	1,237	1,337
First Mortgage Bonds - Series NN [Member]
SUBTOTAL LONG-TERM DEBT	1,505	1,590
First Mortgage Bonds - Series OO [Member]
SUBTOTAL LONG-TERM DEBT	2,107	2,258
First Mortgage Bonds - Series PP [Member]
SUBTOTAL LONG-TERM DEBT	740	780
First Mortgage Bonds - Series QQ [Member]
SUBTOTAL LONG-TERM DEBT	9,915	9,915
First Mortgage Bonds - Series RR [Member]
SUBTOTAL LONG-TERM DEBT	22,500	22,500
First Mortgage Bonds - Series SS [Member]
SUBTOTAL LONG-TERM DEBT	23,000	23,000
First Mortgage Bonds - Series TT [Member]
SUBTOTAL LONG-TERM DEBT	2,258	2,408
First Mortgage Bonds - Series UU [Member]
SUBTOTAL LONG-TERM DEBT	845	890
First Mortgage Bonds - Series VV [Member]
SUBTOTAL LONG-TERM DEBT	2,290	2,433
First Mortgage Bonds - Series WW [Member]
SUBTOTAL LONG-TERM DEBT	830	865
First Mortgage Bonds - Series XX [Member]
SUBTOTAL LONG-TERM DEBT	11,259
First Mortgage Bonds - Series YY [Member]
SUBTOTAL LONG-TERM DEBT	$ 3,860

CONSOLIDATED STATEMENTS OF CAPITAL STOCK AND LONG-TERM DEBT (Parenthetical) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Common Stock, Shares Authorized	40,000,000	40,000,000
Common Stock, Shares Outstanding	16,352,000	16,296,000
Preferred Stock, Shares Authorized	126,000	126,000
Preferred Stock, Shares Outstanding	24,000	24,000
Convertible Preferred Stock $7.00 Series
Common Stock, Shares Outstanding	10,000	10,000
Convertible Preferred Stock $8.00 Series [Member]
Common Stock, Shares Outstanding	3,000	3,000
Nonredeemable Preferred Stock $7.00 Series
Common Stock, Shares Outstanding	1,000	1,000
Nonredeemable Preferred Stock $4.75 Series [Member]
Common Stock, Shares Outstanding	10,000	10,000
Amortizing Secured Note, due December 20, 2021 [Member]
Due date of debt	Dec. 20, 2021
Interest rate	8.05%
Amortizing Secured Note, due May 19, 2028 [Member]
Due date of debt	May 19, 2028
Interest rate	6.25%
Amortizing Secured Note, due August 25, 2030 [Member]
Due date of debt	Aug. 25, 2030
Interest rate	6.44%
Amortizing Secured Note, due September 19, 2031 [Member]
Due date of debt	Sep. 19, 2031
Interest rate	6.46%
State Revolving Trust Note, due December 31, 2022 [Member]
Due date of debt	Dec. 31, 2022
Interest rate	4.22%
State Revolving Trust Note, due May 1, 2025 [Member]
Due date of debt	May 01, 2025
Interest rate	3.60%
State Revolving Trust Note, due March 1, 2026 [Member]
Due date of debt	Mar. 01, 2026
Interest rate	3.30%
State Revolving Trust Note2 [Member]
Due date of debt	Jan. 25, 2027
Interest rate	3.49%
State Revolving Trust Note, due December 1, 2026 [Member]
Due date of debt	Dec. 01, 2026
Interest rate	4.03%
State Revolving Trust Bond 4.00% to 5.00%, due August 1, 2021 [Member]
Due date of debt	Aug. 01, 2021
State Revolving Trust Bond 4.00% to 5.00%, due August 1, 2021 [Member] \| Minimum [Member]
Interest rate	4.00%
State Revolving Trust Bond 4.00% to 5.00%, due August 1, 2021 [Member] \| Maximum [Member]
Interest rate	5.00%
State Revolving Trust Bond 0.00%, due August 1, 2021 [Member]
Due date of debt	Aug. 01, 2021
Interest rate	0.00%
State Revolving Trust Note, due July 1, 2028 [Member]
Due date of debt	Jul. 01, 2028
Interest rate	3.64%
State Revolving Trust Note, due January 1, 2028 [Member]
Due date of debt	Jan. 01, 2028
Interest rate	3.64%
State Revolving Trust Note, due August 1, 2031 [Member]
Due date of debt	Aug. 01, 2031
Interest rate	3.45%
Amortizing Secured Note, due April 20, 2029 [Member]
Due date of debt	Apr. 20, 2029
Interest rate	6.59%
Amortizing Secured Note 7.05%, due January 20, 2030 [Member]
Due date of debt	Jan. 20, 2030
Interest rate	7.05%
Amortizing Secured Note 5.69%, due January 20, 2030 [Member]
Due date of debt	Jan. 20, 2030
Interest rate	5.69%
4.45%, Amortizing Secured Note, due April 20, 2040 [Member]
Due date of debt	Apr. 20, 2040
Interest rate	4.45%
4.47%, Amortizing Secured Note, due April 20, 2040 [Member]
Due date of debt	Apr. 20, 2040
Interest rate	4.47%
State Revolving Trust Note, due July 1, 2031 [Member]
Due date of debt	Jul. 01, 2031
Interest rate	3.75%
State Revolving Trust Note, due February 1, 2036 [Member]
Due date of debt	Feb. 01, 2036
Interest rate	2.00%
State Revolving Trust Note, due November 30, 2030 [Member]
Due date of debt	Nov. 30, 2030
Interest rate	3.75%
Construction Loans [Member]
Interest rate	0.00%
First Mortgage Bonds - Series X [Member]
Due date of debt	Aug. 01, 2018
Interest rate	0.00%
First Mortgage Bonds - Series Y [Member]
Due date of debt	Aug. 01, 2018
First Mortgage Bonds - Series Y [Member] \| Minimum [Member]
Interest rate	4.25%
First Mortgage Bonds - Series Y [Member] \| Maximum [Member]
Interest rate	4.63%
First Mortgage Bonds - Series Z [Member]
Due date of debt	Aug. 01, 2019
Interest rate	0.00%
First Mortgage Bonds - Series AA [Member]
Due date of debt	Aug. 01, 2019
First Mortgage Bonds - Series AA [Member] \| Minimum [Member]
Interest rate	5.25%
First Mortgage Bonds - Series AA [Member] \| Maximum [Member]
Interest rate	5.75%
First Mortgage Bonds - Series BB [Member]
Due date of debt	Aug. 01, 2021
Interest rate	0.00%
First Mortgage Bonds - Series CC [Member]
Due date of debt	Aug. 01, 2021
First Mortgage Bonds - Series CC [Member] \| Minimum [Member]
Interest rate	4.00%
First Mortgage Bonds - Series CC [Member] \| Maximum [Member]
Interest rate	5.00%
First Mortgage Bonds - Series EE [Member]
Due date of debt	Aug. 01, 2023
Interest rate	0.00%
First Mortgage Bonds - Series FF [Member]
Due date of debt	Aug. 01, 2024
First Mortgage Bonds - Series FF [Member] \| Minimum [Member]
Interest rate	3.00%
First Mortgage Bonds - Series FF [Member] \| Maximum [Member]
Interest rate	5.50%
First Mortgage Bonds - Series GG [Member]
Due date of debt	Aug. 01, 2026
Interest rate	0.00%
First Mortgage Bonds - Series HH [Member]
Due date of debt	Aug. 01, 2026
First Mortgage Bonds - Series HH [Member] \| Minimum [Member]
Interest rate	4.00%
First Mortgage Bonds - Series HH [Member] \| Maximum [Member]
Interest rate	5.00%
First Mortgage Bonds - Series II [Member]
Due date of debt	Aug. 01, 2024
Interest rate	0.00%
First Mortgage Bonds - Series JJ [Member]
Due date of debt	Aug. 01, 2027
First Mortgage Bonds - Series JJ [Member] \| Minimum [Member]
Interest rate	3.40%
First Mortgage Bonds - Series JJ [Member] \| Maximum [Member]
Interest rate	5.00%
First Mortgage Bonds - Series KK [Member]
Due date of debt	Aug. 01, 2028
Interest rate	0.00%
First Mortgage Bonds - Series LL [Member]
Due date of debt	Aug. 01, 2028
First Mortgage Bonds - Series LL [Member] \| Minimum [Member]
Interest rate	5.00%
First Mortgage Bonds - Series LL [Member] \| Maximum [Member]
Interest rate	5.50%
First Mortgage Bonds - Series MM [Member]
Due date of debt	Aug. 01, 2030
Interest rate	0.00%
First Mortgage Bonds - Series NN [Member]
Due date of debt	Aug. 01, 2030
First Mortgage Bonds - Series NN [Member] \| Minimum [Member]
Interest rate	3.00%
First Mortgage Bonds - Series NN [Member] \| Maximum [Member]
Interest rate	4.375%
First Mortgage Bonds - Series OO [Member]
Due date of debt	Aug. 01, 2031
Interest rate	0.00%
First Mortgage Bonds - Series PP [Member]
Due date of debt	Aug. 01, 2031
First Mortgage Bonds - Series PP [Member] \| Minimum [Member]
Interest rate	2.00%
First Mortgage Bonds - Series PP [Member] \| Maximum [Member]
Interest rate	5.00%
First Mortgage Bonds - Series QQ [Member]
Due date of debt	Oct. 01, 2023
Interest rate	5.00%
First Mortgage Bonds - Series RR [Member]
Due date of debt	Oct. 01, 2038
Interest rate	3.80%
First Mortgage Bonds - Series SS [Member]
Due date of debt	Oct. 01, 2047
Interest rate	4.25%
First Mortgage Bonds - Series TT [Member]
Due date of debt	Aug. 01, 2032
Interest rate	0.00%
First Mortgage Bonds - Series UU [Member]
Due date of debt	Aug. 01, 2032
First Mortgage Bonds - Series UU [Member] \| Minimum [Member]
Interest rate	3.00%
First Mortgage Bonds - Series UU [Member] \| Maximum [Member]
Interest rate	3.25%
First Mortgage Bonds - Series VV [Member]
Due date of debt	Aug. 01, 2033
Interest rate	0.00%
First Mortgage Bonds - Series WW [Member]
Due date of debt	Aug. 01, 2033
First Mortgage Bonds - Series WW [Member] \| Minimum [Member]
Interest rate	3.00%
First Mortgage Bonds - Series WW [Member] \| Maximum [Member]
Interest rate	5.00%
First Mortgage Bonds - Series XX [Member]
Due date of debt	Aug. 01, 2047
Interest rate	0.00%
First Mortgage Bonds - Series YY [Member]
Due date of debt	Aug. 01, 2047
First Mortgage Bonds - Series YY [Member] \| Minimum [Member]
Interest rate	3.00%
First Mortgage Bonds - Series YY [Member] \| Maximum [Member]
Interest rate	5.00%

CONSOLIDATED STATEMENTS OF COMMON STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock [Member]	Retained Earnings [Member]	Total
Balance at Dec. 31, 2014	$ 148,668	$ 48,623	$ 197,291
Balance, shares at Dec. 31, 2014	16,124,000
Net Income		20,028	20,028
Dividend Reinvestment & Common Stock Purchase Plan	$ 1,462		1,462
Dividend Reinvestment & Common Stock Purchase Plan, shares	63,000
Restricted Stock Award, Net - Employees	$ 528		528
Restricted Stock Award, Net - Employees, shares	33,000
Stock Award - Board Of Directors	$ 105		105
Stock Award - Board Of Directors, shares	5,000
Cash Dividends on Common Stock		(12,554)	(12,554)
Cash Dividends on Preferred Stock		(144)	(144)
Common Stock Expenses		(22)	(22)
Balance at Dec. 31, 2015	$ 150,763	55,931	206,694
Balance, shares at Dec. 31, 2015	16,225,000
Net Income		22,742	22,742
Dividend Reinvestment & Common Stock Purchase Plan	$ 1,453		1,453
Dividend Reinvestment & Common Stock Purchase Plan, shares	43,000
Restricted Stock Award, Net - Employees	$ 682		682
Restricted Stock Award, Net - Employees, shares	24,000
Stock Award - Board Of Directors	$ 147		147
Stock Award - Board Of Directors, shares	4,000
Cash Dividends on Common Stock		(13,137)	(13,137)
Cash Dividends on Preferred Stock		(144)	(144)
Balance at Dec. 31, 2016	$ 153,045	65,392	218,437
Balance, shares at Dec. 31, 2016	16,296,000
Net Income		22,809	22,809
Dividend Reinvestment & Common Stock Purchase Plan	$ 1,234		1,234
Dividend Reinvestment & Common Stock Purchase Plan, shares	32,000
Restricted Stock Award, Net - Employees	$ 724		724
Restricted Stock Award, Net - Employees, shares	22,000
Stock Award - Board Of Directors	$ 147		147
Stock Award - Board Of Directors, shares	4,000
Shares Forfeited	$ (30)		(30)
Shares Forfeited, shares	(2,000)
Cash Dividends on Common Stock		(14,002)	(14,002)
Cash Dividends on Preferred Stock		(144)	(144)
Balance at Dec. 31, 2017	$ 155,120	$ 74,055	$ 229,175
Balance, shares at Dec. 31, 2017	16,352,000

Organization, Summary of Significant Accounting Policies and Recent Developments

12 Months Ended

Dec. 31, 2017

Organization Summary Of Significant Accounting Policies And Recent Developments [Abstract]

Organization, Summary of Significant Accounting Policies and Recent Developments

Note 1 – Organization, Summary of Significant Accounting Policies and Recent Developments

(a) Organization - Middlesex Water Company (Middlesex) is the parent company and sole shareholder of Tidewater Utilities, Inc. (Tidewater), Tidewater Environmental Services, Inc. (TESI), Pinelands Water Company (Pinelands Water) and Pinelands Wastewater Company (Pinelands Wastewater) (collectively, Pinelands), Utility Service Affiliates, Inc. (USA), Utility Service Affiliates (Perth Amboy) Inc. (USA-PA) and Twin Lakes Utilities, Inc. (Twin Lakes). Southern Shores Water Company, LLC (Southern Shores) and White Marsh Environmental Systems, Inc. (White Marsh) are wholly-owned subsidiaries of Tidewater.

Middlesex Water Company has operated as a water utility in New Jersey since 1897, in Delaware, through our wholly-owned subsidiary, Tidewater, since 1992 and in Pennsylvania, through our wholly-owned subsidiary, Twin Lakes, since 2009. We are in the business of collecting, treating, distributing and selling water for domestic, commercial, municipal, industrial and fire protection purposes. We also operate New Jersey municipal water, wastewater and storm water systems under contract and provide unregulated water and wastewater services in New Jersey and Delaware through our subsidiaries. Our rates charged to customers for water and wastewater services, the quality of services we provide and certain other matters are regulated in New Jersey, Delaware and Pennsylvania by the New Jersey Board of Public Utilities (NJBPU), Delaware Public Service Commission (DEPSC) and Pennsylvania Public Utilities Commission (PAPUC), respectively. Our USA, USA-PA and White Marsh subsidiaries are not regulated utilities.

Certain reclassifications have been made to the prior year financial statements to conform with current period presentation. The reclassifications are immaterial to the overall presentation of our consolidated financial statements.

(b) Principles of Consolidation – The financial statements for Middlesex and its wholly-owned subsidiaries (the Company) are reported on a consolidated basis. All significant intercompany accounts and transactions have been eliminated. Other financial investments in which the Company holds a 50% or less voting interest and cannot exercise control over the operation and policies of the investments are accounted for under the equity method of accounting. Under the equity method of accounting, the Company records its investment interests in Non-Utility Assets and its percentage share of the earnings or losses of the investees in Other Income (Expense).

(c) System of Accounts – Middlesex, Pinelands Water and Pinelands Wastewater maintain their accounts in accordance with the Uniform System of Accounts prescribed by the NJBPU. Tidewater, TESI and Southern Shores maintain their accounts in accordance with DEPSC requirements. Twin Lakes maintains its accounts in accordance with PAPUC requirements.

(d) Regulatory Accounting - We maintain our books and records in accordance with accounting principles generally accepted in the United States of America. Middlesex and certain of its subsidiaries, which account for 88% of Operating Revenues and 99% of Total Assets, are subject to regulation in the state in which they operate. Those companies are required to maintain their accounts in accordance with regulatory authorities’ rules and guidelines, which may differ from other authoritative accounting pronouncements. In those instances, the Company follows the guidance provided in Accounting Standards Codification (ASC) 980, Regulated Operations.

In accordance with ASC 980, Regulated Operations, costs and obligations are deferred if it is probable that these items will be recognized for rate-making purposes in future rates. Accordingly, we have recorded costs and obligations, which will be amortized over various future periods. Any change in the assessment of the probability of rate-making treatment will require us to change the accounting treatment of the deferred item. We have no reason to believe any of the deferred items that are recorded will be treated differently by the regulators in the future. For additional information, see Note 2 – Rate and Regulatory Matters.

(e) Retirement Benefit Plans - We maintain a noncontributory defined benefit pension plan (Pension Plan) which covers all active employees who were hired prior to April 1, 2007. In addition, the Company maintains an unfunded supplemental plan for its executive officers that are Pension Plan participants. The Company has a retirement benefit plan other than pensions (Other Benefits Plan) for substantially all of its retired employees. Employees hired after March 31, 2007 are not eligible to participate in this plan. Coverage includes healthcare and life insurance.

The Company’s costs for providing retirement benefits are dependent upon numerous factors, including actual plan experience and assumptions of future experience. Retirement benefit plan obligations and expense are determined based on investment performance, discount rates and various other demographic factors related to the population participating in the Company’s retirement benefit plans, all of which can change significantly in future years. For more information on the Company’s Retirement Benefit Plans, see Note 7 – Employee Benefit Plans.

(f) Utility Plant – Utility Plant is stated at original cost as defined for regulatory purposes. Property accounts are charged with the cost of betterments and major replacements of property. Cost includes direct material, labor and indirect charges for pension benefits and payroll taxes. The cost of labor, materials, supervision and other expenses incurred in making repairs and minor replacements and in maintaining the properties is charged to the appropriate expense accounts. At December 31, 2017, there was no event or change in circumstance that would indicate that the carrying amount of any long-lived asset was not recoverable.

(g) Depreciation – Depreciation is computed by each regulated member of the Company utilizing a rate approved by the applicable regulatory authority. The accumulated provision for depreciation is charged with the cost of property retired, less salvage. The following table sets forth the range of depreciation rates for the major utility plant categories used to calculate depreciation for the years ended December 31, 2017, 2016 and 2015. These rates have been approved by the NJBPU, DEPSC or PAPUC:

Source of Supply	1.15% - 3.44%	Transmission and Distribution (T&D):
Pumping	2.00% - 5.39%	T&D – Mains	1.10% - 3.13%
Water Treatment	1.65% - 7.09%	T&D – Services	2.12% - 3.16%
General Plant	2.08% - 17.84%	T&D – Other	1.61% - 4.63%
Wastewater Collection	1.42% - 1.81%

Non-regulated fixed assets consist primarily of office buildings, furniture and fixtures, and transportation equipment. These assets are recorded at original cost and depreciation is calculated based on the estimated useful lives, ranging from 3 to 40 years.

(h) Preliminary Survey and Investigation (PS&I) Costs – In the design of water and wastewater systems that the Company ultimately intends to construct, own and operate certain expenditures are incurred to advance those project activities. These PS&I costs are recorded as deferred charges on the balance sheet because these costs are expected to be recovered through future rates charged to customers as the underlying projects are placed into service as utility plant. If it is subsequently determined that costs for a project recorded as PS&I are not recoverable through rates charged to our customers, the applicable PS&I costs are recorded as Other Expense on the statement of income at that time.

(i) Customers’ Advances for Construction (CAC) – Utility plant and/or cash advances are provided to the Company by customers, real estate developers and builders in order to extend utility service to their properties. These transactions are recorded as CAC. Contractual Refunds of CACs in the form of cash are made by the Company and are based on either additional operating revenues generated from new customers or as new customers are connected to the respective system. After all refunds are made and/or contract terms have expired, any remaining balance is transferred to Contributions in Aid of Construction.

Contributions in Aid of Construction (CIAC) – CIAC include direct non-refundable contributions of utility plant and/or cash and the portion of CAC that becomes non-refundable.

CAC and CIAC are not depreciated in accordance with regulatory requirements. In addition, these amounts reduce the investment base for purposes of setting rates.

(j) Allowance for Funds Used During Construction (AFUDC) - Middlesex and its regulated subsidiaries capitalize AFUDC, which represents the cost of financing projects during construction. AFUDC is added to the construction costs of individual projects exceeding specific cost and construction period thresholds established for each company and then depreciated along with the rest of the utility plant’s costs over its estimated useful life. AFUDC is calculated using each company’s weighted cost of debt and equity as approved in their most recent respective regulatory rate order. The AFUDC rates for the years ended December 31, 2017, 2016 and 2015 for Middlesex and Tidewater are as follows:

	2017	2016	2015
Middlesex	6.73%	6.73%	6.72%
Tidewater	7.92%	7.92%	7.92%

(k) Accounts Receivable – We record bad debt expense based on historical write-offs combined with an evaluation of current conditions. The allowance for doubtful accounts was $0.9 million as of December 31, 2017 and 2016. For the years ended December 31, 2017, 2016 and 2015, bad debt expense was $0.5 million, $0.7 million and $0.8 million, respectively. For the years ended December 31, 2017, 2016 and 2015, write-offs were $0.5 million, $0.6 million and $0.6 million, respectively. Receivables not expected to be received in 2018 are included as non-current assets in Operations Contracts, Developer and Other Receivables, including a loan by Middlesex to Ridgewood Green RME (RGRME).

In 2011, Middlesex entered into a joint venture agreement that established the legal entity RGRME for the purpose of owning and operating a renewable energy facility at a municipal wastewater treatment plant in New Jersey. Construction was completed and the facility began operating in 2013. This public-private partnership includes the production of electricity from solar panels and biogas to meet the electric power needs of the municipal wastewater treatment plant. A major element of the project’s profitability is the ability to procure, and process, an adequate supply of high quality feedstock material from outside sources to supplement the production of biogas. Such feedstock is in the form of fats, oils, grease and other materials from various commercial operations. During the fourth quarter of 2016, RGRME determined that significant additional investment would need to be made to optimize the liquid waste disposal and biogas electricity generation process. As of December 31, 2017, Middlesex had an investment of $0.2 million of equity capital (included in “Non-utility Assets – Net”) and a $1.7 million loan to RGRME (included in “Operations Contracts, Developer and Other Receivables, net”). The Company has determined that it is more likely than not that RGRME will be unable to satisfy its remaining debt service obligation to Middlesex and therefore, an allowance for uncollectible notes receivable of $1.7 million has been recorded. Furthermore, Middlesex has recognized a noncash impairment charge of $0.2 million, representing the Middlesex’s equity investment in RGRME. These charges are included in “Other Expense” for the year ended December 31, 2016 on the consolidated statement of income.

(l) Revenues - Retail customer invoices for regulated utility service are typically comprised of two components; a fixed service charge and a volumetric or consumption charge. Revenues from retail customers, except Tidewater fixed service charges, include amounts billed in arrears on a cycle basis and unbilled amounts estimated from the last meter reading date to the end of the accounting period. The estimated unbilled amounts are determined by utilizing factors which include historical volumetric or consumption usage and current climate and economic conditions. Actual billings may differ from our estimates. Tidewater customers are billed in advance for their fixed service charge and these revenues are recognized as the service is provided to the customer.

Southern Shores is an unmetered system. Customers are billed a fixed service charge in advance at the beginning of each month and revenues are recognized as earned.

Customers in portions of the TESI system are billed a fixed service charge in arrears.

Revenues from White Marsh’s base water and wastewater system operating contracts are fixed, billed monthly and are recorded as earned. White Marsh also provides services in addition to the base services provided under its water and wastewater operating contracts, which are billed and recorded as earned.

Revenues from the City of Perth Amboy management contract are comprised of fixed and variable fees. Fixed fees are billed monthly and recorded as earned. Variable fees are recorded upon approval of the amount by the City of Perth Amboy.

Revenues from USA’s operations and maintenance contract for the Borough of Avalon, New Jersey (Avalon) water utility, sewer utility and storm water system are fixed for the term of the contract, are billed monthly and recorded as earned. USA also provides services to Avalon in addition to the base services provided under the operation and maintenance contract. These additional services are recorded as earned and billed upon approval of Avalon.

(m) Unamortized Debt Expense and Premiums on Long-Term Debt - Unamortized Debt Expense and Premiums on Long-Term Debt, included on the consolidated balance sheet in long-term debt, are amortized over the lives of the related debt issues.

(n) Income Taxes - Middlesex files a consolidated federal income tax return for the Company and income taxes are allocated based on the separate return method. Investment tax credits have been deferred and are amortized over the estimated useful life of the related property. For more information on income taxes, see Note 3 – Income Taxes.

(o) Statements of Cash Flows - For purposes of reporting cash flows, the Company considers all highly liquid investments with original maturity dates of three months or less to be cash equivalents. Cash and cash equivalents represent bank balances and money market funds with investments maturing in less than 90 days.

(p) Restricted Cash – Restricted cash includes cash proceeds from loan transactions entered into through state financing programs and are held in trusts for specific capital expenditures or debt service.

(q) Use of Estimates - Conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts in the financial statements. Actual results could differ from those estimates.

(r) Recent Accounting Pronouncements

Consolidation - In February 2015, the Financial Accounting Standards Board (FASB) issued guidance that amends the consolidation analysis for variable interest entities (“VIEs”) as well as voting interest entities. The amendments under the new guidance modify the evaluation of whether limited partnerships and similar legal entities are VIEs or voting interest entities and eliminate the presumption that a general partner should consolidate a limited partnership. This guidance was effective January 1, 2016. The adoption of this guidance did not have a material impact on the Company’s financial statements.

Debt Issuance Costs - In April 2015, the FASB issued an update to authoritative guidance related to the presentation of debt issuance costs on the balance sheet, requiring companies to present debt issuance costs as a direct deduction from the carrying value of debt. The guidance was effective January 1, 2016. The adoption of this guidance had no impact on the Company’s statements of income or cash flows.

Deferred Income Taxes – In November 2015, the FASB issued guidance on the classification of deferred tax assets and deferred tax liabilities, requiring entities to present them as noncurrent on the balance sheet. This guidance was effective January 1, 2016 and did not have a material impact on the Company’s balance sheet.

Inventory - In July 2015, the FASB issued guidance on simplifying the measurement of inventory. The new guidance replaces the current lower of cost or market test with a lower of cost and net realizable value test when cost is determined on a first-in, first-out or average cost basis. The guidance was effective January 1, 2017 and did not have a material impact on the Company’s financial statements.

Accounting for Share-Based Payments - In March 2016, the FASB issued guidance which simplifies several aspects of the accounting for employee share-based payment transactions, including the accounting for income taxes, forfeitures, and statutory tax withholding requirements, as well as classification in the statement of cash flows. The guidance was effective January 1, 2017 and did not have a material impact on the Company’s financial statements.

Revenue Recognition - In May 2014, the FASB issued guidance, which replaces most of the existing guidance with a single set of principles for recognizing revenue from contracts with customers. This guidance is effective January 1, 2018, at which time the Company will adopt this guidance using the modified retrospective method. The Company has assessed the impact this will have on our financial statements by analyzing our inventory of contracts with customers, which consist primarily of regulated tariff-based sales and non-regulated operation and maintenance contracts for water and wastewater systems. Based on the Company’s interpretation and analysis of this guidance, it will not have a material impact on the Company’s financial statements since it is expected that there will be no material changes to the timing or recognition of revenue. Adoption of this guidance will result in more detailed revenue disclosures than currently required under existing guidance.

Recognition and Measurement of Financial Assets and Financial Liabilities - In January 2016, the FASB issued guidance which (i) requires all investments in equity securities, including other ownership interests such as partnerships, unincorporated joint ventures and limited liability companies, to be carried at fair value through net income, (ii) requires an incremental recognition and disclosure requirement related to the presentation of fair value changes of financial liabilities for which the fair value option has been elected, (iii) amends several disclosure requirements, including the methods and significant assumptions used to estimate fair value or a description of the changes in the methods and assumptions used to estimate fair value, and (iv) requires disclosure of the fair value of financial assets and liabilities measured at amortized cost at the amount that would be received to sell the asset or paid to transfer the liability. The guidance is effective for fiscal years beginning after December 15, 2017. The guidance is required to be applied retrospectively with a cumulative effect adjustment to retained earnings for initial application of the guidance at the date of adoption (modified retrospective method). The Company does not expect that the adoption of this guidance to have a material impact on the Company’s financial statements.

Statement of Cash Flows - In August 2016, the FASB issued guidance which amends the previous guidance on the classification of certain cash receipts and payments in the statement of cash flows. The primary purpose of the amendment is to reduce the diversity in practice that has resulted from the lack of consistent principles on this topic. The guidance is effective January 1, 2018 and its adoption is not expected to have a material impact on the Company’s financial statements.

Restricted Cash - In November 2016, the FASB issued guidance related to the classification and presentation of restricted cash in the statement of cash flows, which requires entities to a) include restricted cash balances in its cash and cash-equivalent balances in the statement of cash flows and b) include a reconciliation of cash and cash-equivalents per the statement of financial position as compared to the statement of cash flows. Changes in restricted cash and restricted cash equivalents that result from transfers between cash, cash equivalents, and restricted cash and restricted cash equivalents will not be presented as cash flow activities in the statement of cash flows. In addition, an entity with a material balance of amounts described as restricted cash and restricted cash equivalents must disclose information about the nature of the restrictions. The guidance is effective January 1, 2018 and its adoption is not expected to have a material impact on the Company’s financial statements.

Employee Benefit Plans-Net Periodic Benefit Cost – In March 2017, the FASB issued guidance which requires entities to (1) disaggregate the current-service-cost component from the other components of net benefit cost and present it with other current compensation costs for related employees in the income statement and (2) present the

other components elsewhere in the income statement and outside of income from operations if that subtotal is presented. In addition, the guidance requires entities to disclose the income statement lines that contain the other components if they are not presented on appropriately described separate lines. The guidance is effective January 1, 2018. The Company does not expect that the adoption of this guidance to have a material impact on the Company’s financial statements.

Leases - In February 2016, the FASB issued guidance related to leases which will require lessees to recognize a lease liability (a lessee’s obligation to make lease payments arising from a lease, measured on a discounted basis) a right-of-use asset (an asset that represents the lessee’s right to use, or control the use of, a specified asset for the lease term). The guidance is effective for fiscal years beginning after December 15, 2018 with early adoption permitted. The Company is currently assessing the impact of this standard on its consolidated financial statements and footnote disclosures, but, based on the Company’s current leasing activity, does not expect that the adoption of this guidance to have a material impact on the Company’s financial statements.

There are no other new adopted or proposed accounting guidance that the Company is aware of that could have a material impact on the Company’s financial statements.

Rate and Regulatory Matters

12 Months Ended

Dec. 31, 2017

Regulated Operations [Abstract]

Rate and Regulatory Matters

Note 2 - Rate and Regulatory Matters

Rate Matters

Middlesex - In October 2017, Middlesex filed a petition with the New Jersey Board of Public Utilities (NJBPU) seeking permission to increase base water rates by approximately $15.3 million per year. The request was necessitated by capital infrastructure investments Middlesex has made, or has committed to make, to drinking water infrastructure since the last filing in New Jersey in 2015 as well as increased operations and maintenance costs. We cannot predict when and whether the NJBPU will ultimately approve, deny, or reduce the amount of the request. Under New Jersey statute, the NJBPU must render a decision within nine months of filing a petition.

In October 2017, the NJBPU approved Middlesex’s petition to reset its Purchased Water Adjustment Clause (PWAC) tariff rate to recover additional annual costs of $1.2 million, primarily for the purchase of untreated water from the New Jersey Water Supply Authority. A PWAC is a rate mechanism that allows for the recovery of increased purchased water costs between base rate case filings. The PWAC is reset to zero once those increased costs are included in base rates. The reset PWAC tariff rate became effective on November 1, 2017.

In August 2015, Middlesex implemented a $5.0 million NJBPU-approved rate increase. The rate increase was needed to recover increased costs and lost customer revenues, as well as a return on invested capital in rate base of $219.0 million, based on a return on equity of 9.75%.

Tidewater - Effective January 1, 2018, Tidewater increased its Delaware Public Service Commission (DEPSC) approved Distribution System Improvement Charge rate, which is expected to generate revenues of approximately $0.4 million annually.

Pinelands - In April 2016, the NJBPU approved $0.2 million and $0.1 million of increases, respectively, in Pinelands Water and Pinelands Wastewater’s annual base rates, effective May 7, 2016. The rate increases were necessitated by capital infrastructure investments by the companies, increased operations and maintenance costs and lower non-fixed fee revenues. The Pinelands Water base water rate increase was phased-in between 2016 and 2017.

Southern Shores - Under the terms of a multi-year DEPSC-approved agreement expiring in 2020, customer rates will increase on January 1^st of each year to generate additional annual revenue of $0.1 million with each increase.

Twin Lakes - In June 2016, the Pennsylvania Public Utilities Commission approved a $0.1 million increase in Twin Lakes’ base water rates. The rate increase was necessitated by capital infrastructure investments Twin Lakes has made, or committed to make, and increased operations and maintenance costs. The rate increase will be phased in with the final phase implemented subsequent to specific capital investments being placed in service.

Regulatory Matters

We have recorded certain costs as regulatory assets because we expect full recovery of, or are currently recovering, these costs in the rates we charge customers. These deferred costs have been excluded from rate base and, therefore, we are not earning a return on the unamortized balances. These items are detailed as follows:

	(Thousands of Dollars)
	December 31,				Remaining
Regulatory Assets	2017		2016		Recovery Periods
Retirement Benefits	$	43,070	$	40,603	Various
Income Taxes		9,876		15,899	Various
Rate Cases, Tank Painting, and Other		5,477		4,392	2-10 years
Total	$	58,423	$	60,894

Retirement benefits include pension and other retirement benefits that have been recorded on the Consolidated Balance Sheet in accordance with the guidance provided in ASC 715, Compensation – Retirement Benefits. These amounts represent obligations in excess of current funding, which the Company believes will be fully recovered in rates set by the regulatory authorities.

The recovery period for income taxes is dependent upon when the temporary differences between the tax and book treatment of various items reverse.

On December 22, 2017, the Tax Cuts and Jobs Act of 2017 (the Tax Act) was signed into law making significant changes to the Internal Revenue Code, including a corporate tax rate decrease from 35% to 21% effective for tax years beginning after December 31, 2017. The tariff rates charged to customers in the Company’s regulated companies, which comprise 92% of the Company’s 2017 pre-tax income, include recovery of income taxes at the statutory rate at the time those rates are approved by the respective state public utility commissions that regulate each of our regulated subsidiaries. The Company is currently performing a revaluation of its deferred income tax liabilities to comply with orders issued by the NJBPU and the DEPSC seeking information on the amount of income taxes collected in rates that are not expected to be incurred by the Company and the proposed methodology to adjust rates charged to customers to reflect excess taxes collected and the decreased corporate tax rate. The revaluation is based on certain assumptions and estimations made in accordance with the Company’s understanding of the Tax Act and the authoritative guidance available as of the date of this filing. Initially, the Company has recorded regulatory liabilities of $31.6 million and reduced its income tax related regulatory assets $5.9 million for the revaluation of its deferred income taxes pertaining to rate-regulated operations. If new or revised authoritative guidance were to change the Company’s understanding of the Tax Act impact on rate-regulated income taxes, it will update its accounting accordingly. The regulatory liabilities are overwhelmingly related to utility plant depreciation deduction timing differences, which are subject to Internal Revenue Service (IRS) normalization rules. The IRS requires that any utility plant related excess taxes cannot be returned to customers any faster than over the remaining life of the underlying utility plant.

The Company uses composite depreciation rates for its regulated utility assets, which is currently an acceptable method under generally accepted accounting principles and is widely used in the utility industry. Historically, under the composite depreciation method, the anticipated costs of removing assets upon retirement are provided for over the life of those assets as a component of depreciation expense. The Company recovers certain asset retirement costs through rates charged to customers as an approved component of depreciation expense. As of December 31, 2017 and 2016, the Company has approximately $12.2 million and $11.3 million, respectively, of expected costs of removal recovered currently in rates in excess of actual costs incurred as regulatory liabilities.

The Company is recovering through customer rates acquisition premiums totaling $0.5 million over the remaining lives of the underlying Utility Plant. These deferred costs have been included in rate base as utility plant and a return is being earned on the unamortized balances during the recovery periods.

Income Taxes

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Income Taxes

Note 3 – Income Taxes

Income tax expense differs from the amount computed by applying the statutory rate on book income subject to tax for the following reasons:

	(Thousands of Dollars)
	Years Ended December 31,
	2017			2016			2015
Income Tax at Statutory Rate	$	11,868		$	12,007		$	10,703
Tax Effect of:
Utility Plant Related		(1,016	)		(1,059	)		(920	)
State Income Taxes – Net		895			770			745
Tax Act		(610	)		—			—
Employee Benefits		(43	)		(5	)		7
Other		6			22			16
Total Income Tax Expense	$	11,100		$	11,735		$	10,551

Income tax expense is comprised of the following:

	(Thousands of Dollars)
	Years Ended December 31,
	2017			2016			2015
Current:
Federal	$	2,090		$	7,305		$	(15,203	)
State		1,066			877			1,153
Deferred:
Federal		7,713			3,325			24,686
State		310			307			(6	)
Investment Tax Credits		(79	)		(79	)		(79	)
Total Income Tax Expense	$	11,100		$	11,735		$	10,551

Deferred income taxes reflect the net tax effect of temporary differences between the carrying amounts of assets and liabilities for financial purposes and the amounts used for income tax purposes. The components of the net deferred tax liability are as follows:

	(Thousands of Dollars)
	December 31,
	2017			2016
Utility Plant Related	$	41,259		$	69,019
Customer Advances		(3,749	)		(3,430	)
Employee Benefits		4,903			6,904
Investment Tax Credits (ITC)		675			753
Other		72			(421	)
Total Deferred Tax Liability and ITC	$	43,160		$	72,825

The staff of the United States Securities and Exchange Commission (SEC) has recognized the complexity of reflecting the impacts of the Tax Act, and on December 22, 2017 issued guidance in Staff Accounting Bulletin 118 (SAB 118) which clarifies accounting for income taxes if information is not yet available or complete and provides for up to a one year period in which to complete the required analyses and accounting. SAB 118 describes three scenarios or buckets associated with a company’s status of accounting for income tax reform: (1) a company is complete with its accounting for certain effects of tax reform, (2) a company is able to determine a reasonable estimate for certain effects of tax reform and records that estimate as a provisional amount, or (3) a company is not able to determine a reasonable estimate and therefore continues to account for income taxes based on the provisions of the tax laws that were in effect immediately prior to the Tax Act being enacted. The Company has made a reasonable estimate for the measurement and accounting of the effects of the Tax Act which have been reflected in the December 31, 2017 financial statements. However, the final impact of the Tax Act may differ from these estimates due to, among other things, changes in the Company’s interpretations and assumptions and additional guidance that may be issued by the IRS, the Company’s rate regulators or the FASB. The re-measurement of deferred income taxes at the new federal tax rate decreased deferred income tax expense by $0.6 million for the year ending December 31, 2017. Additionally, the re-measurement of deferred income taxes decreased accumulated deferred income taxes by $24.2 million as of December 31, 2017.

As part of its 2014 Federal income tax return, the Company adopted the final IRS regulations pertaining to the tax deductibility of costs that qualify as repairs on tangible property. The adoption resulted in a net reduction of $17.6 million in taxes previously remitted to the IRS, for which the Company has already sought and received refunds pertaining to tax years 2012 through 2014 in accordance with IRS regulations. Subsequently, the Company’s 2014 federal income tax return was selected for examination by the IRS. Concurrently with the IRS examination, the Company agreed to extend the statutory review period for its 2012 thru 2014 tax years. It is unknown at this time whether the results of this examination will result in any changes to the filed 2014 tax return. While the Company believes that its treatment of qualifying tangible property repair costs is proper, its deductibility could be challenged as part of the current examination by the IRS. Therefore, the Company has recorded a provision against refundable taxes of $2.3 million.

It is probable that any net tax benefits that resulted from adopting the regulations will be considered in determining the revenue requirement in the Company’s current rate increase petition (see Note 2 - Rate and Regulatory Matters).

The statutory review periods for income tax returns for the years prior to 2012 have been closed. In the event that there are interest and penalties associated with income tax adjustments in the current examination and future examinations, these amounts will be reported under interest expense and other expense, respectively. Other than the effects of the provision against refundable taxes discussed above, there are no unrecognized tax benefits resulting from prior period tax positions.

Commitments and Contingent Liabilities

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingent Liabilities

Note 4 - Commitments and Contingent Liabilities

Water Supply - Middlesex has an agreement with the New Jersey Water Supply Authority (NJWSA) for the purchase of untreated water through November 30, 2023, which provides for an average purchase of 27.0 million gallons a day (mgd). Pricing is set annually by the NJWSA through a public rate making process. The agreement has provisions for additional pricing in the event Middlesex overdrafts or exceeds certain monthly and annual thresholds.

Middlesex also has an agreement with a non-affiliated regulated water utility for the purchase of treated water. This agreement, which expires February 27, 2021, provides for the minimum purchase of 3.0 mgd of treated water with provisions for additional purchases.

Tidewater contracts with the City of Dover, Delaware to purchase treated water of 15.0 million gallons annually.

Purchased water costs are shown below:

	(Millions of Dollars)
	Years Ended December 31,
Purchased Water	2017		2016		2015
Untreated	$	2.8	$	2.6	$	2.5
Treated		3.3		3.2		3.1
Total Costs	$	6.1	$	5.8	$	5.6

Contract Operations - USA-PA operates the City of Perth Amboy, New Jersey’s (Perth Amboy) water and wastewater collection systems under a 20-year agreement, which expires on December 31, 2018. In connection with the agreement with Perth Amboy, USA-PA entered into a 20-year subcontract with a wastewater operating company for the operation and maintenance of the Perth Amboy wastewater collection system. The subcontract provides for the sharing of certain fixed and variable fees and operating expenses and its term is concurrent with USA-PA’s contract with Perth Amboy.

Guarantees - As part of an agreement with the County of Monmouth, New Jersey (County), Middlesex serves as guarantor of the performance of Applied Water Management, Inc. (AWM), an unaffiliated wastewater treatment contractor, to operate a County-owned leachate pretreatment facility at the Monmouth County Reclamation Center in Tinton Falls, New Jersey. The performance guaranty is effective through 2028 unless another guarantor, acceptable to the County, replaces Middlesex before such date. Under agreements with AWM and Natural Systems Utilities, LLC (NSU), the parent company of AWM, Middlesex earns a fee for providing the performance guaranty. In addition, Middlesex may provide operational support to the facility, as needed, and AWM and NSU, serving as guarantor to Middlesex with respect to the performance of AWM, agree to indemnify Middlesex against any claims that may arise under the Middlesex guaranty to the County.

If requested to perform under the guaranty to the County and, if AWM and NSU, as guarantor to Middlesex, do not fulfill their obligations to indemnify Middlesex against any claims that may arise under the Middlesex guaranty to the County, Middlesex would be required to fulfill the remaining operational commitment of AWM. As of December 31, 2017 and December 31, 2016, the liability recognized in Other Non-Current Liabilities on the balance sheet for the guaranty is approximately $0.1 million.

Leases - The Company has entered into office space operating leases. Rental expenses under operating leases were $0.1 million for the year ended December 31, 2017. The Company did not incur rental expenses for the years ended December 31, 2016 and 2015. The operating leases for these facilities will expire in 2027 and 2028. The minimum annual future rental commitment under operating leases that have initial or remaining non-cancelable lease terms over the next 5 years and thereafter are as follows:

Year	(Millions of Dollars) Annual Maturities
2018	$ 0.7
2019	$ 0.7
2020	$ 0.7
2021	$ 0.7
2022	$ 0.7
Thereafter	$ 3.8

Construction –The Company has projected to spend approximately $94 million in 2018, $94 million in 2019 and $79 million in 2020 on its construction program. The actual amount and timing of capital expenditures is dependent on the need for replacement of existing infrastructure, customer growth, residential new home construction and sales, project scheduling and continued refinement of project scope and costs. There is no assurance that projected customer growth and residential new home construction and sales will occur.

Litigation – The Company is a defendant in lawsuits in the normal course of business. We believe the resolution of pending claims and legal proceedings will not have a material adverse effect on the Company’s consolidated financial statements.

Change in Control Agreements – The Company has Change in Control Agreements with certain of its officers that provide compensation and benefits in the event of termination of employment in connection with a change in control of the Company.

Short-term Borrowings

12 Months Ended

Dec. 31, 2017

Short-term Debt [Abstract]

Short-term Borrowings

Note 5 – Short-term Borrowings

Information regarding the Company’s short-term borrowings for the years ended December 31, 2017 and 2016 is summarized below:

	(Millions of Dollars)
	2017			2016
Established Lines at Year-End	$	92.0		$	60.0
Maximum Amount Outstanding		28.0			13.1
Average Outstanding		18.6			7.4
Notes Payable at Year-End		28.0			12.0
Weighted Average Interest Rate		2.15	%		1.54	%
Weighted Average Interest Rate at Year-End		2.54	%		1.71	%

The maturity dates for the Notes Payable as of December 31, 2017 are in January 2018 through March 2018 and are extendable at the discretion of the Company.

Interest rates for short-term borrowings are below the prime rate with no requirement for compensating balances.

Capitalization

12 Months Ended

Dec. 31, 2017

CAPITALIZATION:

Capitalization

Note 6 - Capitalization

All the transactions discussed below related to the issuance of securities were approved by either the NJBPU or DEPSC, except where otherwise noted.

Common Stock

The Company periodically issues shares of its common stock in connection with its Middlesex Water Company Investment Plan (the Investment Plan), a direct share purchase and sale and dividend reinvestment plan for Middlesex common stock. In July 2015, the Company registered an additional 700,000 common shares for potential issuance under the Investment Plan with the SEC, increasing the number of NJBPU-authorized shares to 3.0 million. The cumulative number of shares issued under the Investment Plan at December 31, 2017 is 2.4 million. For the years ended December 31, 2017, 2016 and 2015, the Company raised approximately $1.2 million, $1.5 million and $1.5 million, respectively, through the issuance of shares under the Investment Plan.

The Company issues shares under a restricted stock plan for certain management employees, which is described in Note 7 – Employee Benefit Plans.

The Company maintains a stock plan for its outside directors (the Outside Director Stock Compensation Plan). For the years ended December 31, 2017, 2016 and 2015, 3,976, 3,976 and 4,795 shares, respectively, of Middlesex common stock were granted and issued to the Company’s outside directors under the Outside Director Stock Compensation Plan and 64,168 shares remain available for future awards. The maximum number of shares authorized for grant under the Outside Director Stock Compensation Plan is 100,000.

In the event dividends on the preferred stock are in arrears, no dividends may be declared or paid on the common stock of the Company.

Preferred Stock

At December 31, 2017 and 2016, there were 0.1 million shares of preferred stock authorized and less than 0.1 million shares of preferred stock outstanding. There were no preferred stock dividends in arrears.

The Company may not pay any dividends on its common stock unless full cumulative dividends to the preceding dividend date for all outstanding shares of preferred stock have been paid or set aside for payment. If four or more quarterly dividends are in arrears, the preferred shareholders, as a class, are entitled to elect two members to the Board of Directors in addition to Directors elected by holders of the common stock. In addition, if Middlesex were to liquidate, holders of preferred stock would be paid back the stated value of their preferred shares before any distributions could be made to common stockholders.

The conversion feature of the no par $7.00 Series Cumulative and Convertible Preferred Stock allows the security holders to exchange one convertible preferred share for twelve shares of the Company's common stock. In addition, the Company may redeem up to 10% of the outstanding convertible stock in any calendar year at a price equal to the fair value of twelve shares of the Company's common stock for each share of convertible stock redeemed.

The conversion feature of the no par $8.00 Series Cumulative and Convertible Preferred Stock allows the security holders to exchange one convertible preferred share for 13.714 shares of the Company's common stock. The preferred shares are convertible into common stock at the election of the security holder or Middlesex.

Long-term Debt

Subject to regulatory approval, the Company periodically issues long-term debt to fund its investments in utility plant and other assets. To the extent possible, the Company finances qualifying capital projects under State Revolving Fund (SRF) loan programs in New Jersey and Delaware. These government programs provide financing at interest rates that are typically below rates available in the broader financial markets. A portion of the borrowings under the New Jersey SRF is interest-free. Under the New Jersey SRF program, borrowers first enter into a construction loan agreement with the New Jersey Infrastructure Bank (NJIB) at a below market interest rate. The NJIB was formally known as the New Jersey Environmental Infrastructure Trust. The current interest rate on construction loan borrowings is zero percent (0%). When construction on the qualifying project is substantially complete, NJIB will coordinate the conversion of the construction loan into a long-term securitized loan with a portion of the principal balance having a stated interest rate of zero percent (0%) and a portion of the principal balance at a market interest rate at the time of closing using the credit rating of the State of New Jersey. The current term of the long-term loans offered through the NJIB is up to thirty years. The current portion of the principal balance having a stated interest rate of zero percent (0%) is 75% with the remaining portion of 25% having a market based interest rate. NJIB generally schedules its long-term debt financings in May and November.

Middlesex closed on a $9.5 million NJBPU approved NJIB construction loan in August 2017. The proceeds are being used to fund the RENEW 2017 project. Through December 31, 2017, Middlesex has drawn down $3.9 million and expects to draw down the remaining proceeds during the first quarter of 2018. The NJIB has notified the Company that the RENEW 2017 construction loan is scheduled for the May 2018 long-term debt financing program.

In November 2017, Middlesex closed out three of its active NJIB construction loans (booster station upgrade, RENEW 2015 and RENEW 2016 projects) by issuing to the NJIB first mortgage bonds designated as Series XX ($11.3 million) and Series YY ($3.9 million). The interest rate on the Series XX bond will be zero and the interest rate on the Series YY bond range between 3.0% and 5.0%. Through December 31, 2017, Middlesex has drawn down $14.2 million and expects to draw down the remaining proceeds during the first quarter of 2018. The final maturity date for both bonds will be August 1, 2047, with scheduled principal and interest payments over the life of the loans.

In February 2016, Tidewater closed on a $1.2 million General Obligation Note loan with the Delaware SRF program to fund the replacement of the water distribution system in a manufactured home community. Tidewater has drawn $1.1 million on this loan and the project is considered complete. The interest rate on the $1.1 million is 2.0% with a final repayment maturity date of February 1, 2036.

In 2015, Tidewater completed the drawdown of a $15.0 million long-term debt transaction. The interest rate on $11.0 million of the loan is 4.45%. $4.0 million of the loan was initially set up as a market-based variable interest rate transaction, but which was converted to a fixed rate of 4.47% in January 2017. The proceeds were used to pay down short-term debt and for other general corporate purposes. The final maturity date of all borrowings under this loan agreement is April 2040.

Bond Series QQ, RR and SS are term bonds with single maturity dates subsequent to 2022. Principal repayments for all series of the Company’s long-term debt except for Bond Series X, Y, Z, AA, BB and CC extend beyond 2022. The aggregate annual principal repayment obligations for all long-term debt over the next five years are shown below:

Year	(Millions of Dollars) Annual Maturities
2018	$ 6.9
2019	$ 7.1
2020	$ 6.9
2021	$ 6.9
2022	$ 6.4

The weighted average interest rate on all long-term debt at December 31, 2017 and 2016 was 3.77% and 3.88%, respectively. Except for the Amortizing Secured Notes ($39.6 million), all of the Company’s outstanding long-term debt has been issued through the New Jersey Economic Development Authority ($55.4 million), the NJIB program ($43.8 million) and the Delaware SRF program ($9.1 million).

In both 2016 and 2015, the NJIB de-obligated principal payments of $0.5 million on several series of SRF long-term debt.

Substantially all of the utility plant of the Company is subject to the lien of its mortgage, which includes debt service and capital ratio covenants. The Company is in compliance with all of its mortgage covenants and restrictions.

Earnings Per Share

The following table presents the calculation of basic and diluted earnings per share (EPS) for the three years ended December 31, 2017. Basic EPS is computed on the basis of the weighted average number of shares outstanding. Diluted EPS assumes the conversion of both the Convertible Preferred Stock $7.00 Series and $8.00 Series.

	(In Thousands, Except Per Share Amounts)
	2017					2016					2015
Basic:	Income			Shares		Income			Shares		Income			Shares
Net Income	$	22,809			16,330	$	22,742			16,270	$	20,028			16,175
Preferred Dividend		(144	)				(144	)				(144	)
Earnings Applicable to Common Stock	$	22,665			16,330	$	22,598			16,270	$	19,884			16,175
Basic EPS	$	1.39				$	1.39				$	1.23
Diluted:
Earnings Applicable to Common Stock	$	22,665			16,330	$	22,598			16,270	$	19,884			16,175
$7.00 Series Dividend		67			115		67			115		67			115
$8.00 Series Dividend		24			41		24			41		24			41
Adjusted Earnings Applicable to Common Stock	$	22,756			16,486	$	22,689			16,426	$	19,975			16,331
Diluted EPS	$	1.38				$	1.38				$	1.22

Fair Value of Financial Instruments

The following methods and assumptions were used by the Company in estimating its fair value disclosure for financial instruments for which it is practicable to estimate that value. The carrying amounts reflected in the consolidated balance sheets for cash and cash equivalents, accounts receivable, accounts payable and notes payable approximate their respective fair values due to the short-term maturities of these instruments. The fair value of First Mortgage and State Revolving Fund Bonds (collectively, the Bonds) issued by Middlesex is based on quoted market prices for similar issues. Under the fair value hierarchy, the fair value of cash and cash equivalents is classified as a Level 1 measurement and the fair value of notes payable and the Bonds in the table below are classified as Level 2 measurements. The carrying amount and fair value of the Bonds were as follows:

	(Thousands of Dollars)
	At December 31,
	2017				2016
	Carrying		Fair		Carrying		Fair
	Amount		Value		Amount		Value
Bonds	$	95,322	$	98,036	$	82,786	$	84,821

For other long-term debt issuances for which there is no quoted market price and there is not an active trading market, it was not practicable to estimate their fair value. For details, including carrying value, interest rate and due date on these series of long-term debt, please refer to those series of long-term debt described as “Amortizing Secured Note”, “State Revolving Trust Note” and “Construction Loans” on the Condensed Consolidated Statements of Capital Stock and Long-Term Debt). The carrying amount of these instruments was $52.5 million and $59.7 million at December 31, 2017 and December 31, 2016, respectively. Customer advances for construction have carrying amounts of $21.4 million and $20.8 million at December 31, 2017 and December 31, 2016, respectively. Their relative fair values cannot be accurately estimated since future refund payments depend on several variables, including new customer connections, customer consumption levels and future rate increases.

Employee Benefit Plans

12 Months Ended

Dec. 31, 2017

Retirement Benefits [Abstract]

Employee Benefit Plans

Note 7 - Employee Benefit Plans

Pension Benefits

The Company’s Pension Plan covers all active employees hired prior to April 1, 2007. Employees hired after March 31, 2007 are not eligible to participate in this plan, but can participate in a defined contribution profit sharing plan that provides an annual contribution at the discretion of the Company, based upon a percentage of

the participants’ annual paid compensation. In order to be eligible for contribution, the eligible employee must be employed by the Company on December 31^st of the year to which the contribution relates. The Company maintains an unfunded supplemental plan for its executive officers. The Accumulated Benefit Obligation for the Company’s Pension Plan at December 31, 2017 and 2016 was $75.7 million and $66.8 million, respectively.

Other Benefits

The Company’s Other Benefits Plan covers substantially all of its current retired employees. Employees hired after March 31, 2007 are not eligible to participate in this plan. Coverage includes healthcare and life insurance. Accrued retirement benefit costs are recorded each year.

Regulatory Treatment of Over/Underfunded Retirement Obligations

Because the Company is subject to regulation in the states in which it operates, it is required to maintain its accounts in accordance with the regulatory authority’s rules and guidelines, which may differ from other authoritative accounting pronouncements. In those instances, the Company follows the guidance of ASC 980, Regulated Operations. Based on prior regulatory practice, and in accordance with the guidance in ASC 980, Regulated Operations, the Company records underfunded Pension Plan and Other Benefits Plan obligation costs, which otherwise would be recognized in Other Comprehensive Income under ASC 715, Compensation – Retirement Benefits, as a Regulatory Asset, and expects to recover those costs in rates charged to customers.

The Company uses a December 31 measurement date for all of its employee benefit plans. The tables below set forth information relating to the Company’s Pension Plan and Other Benefits Plan for 2017 and 2016.

	(Thousands of Dollars)
	Pension Plan						Other Benefits Plan
	December 31,
	2017			2016			2017			2016
Change in Projected Benefit Obligation:
Beginning Balance	$	78,601		$	72,542		$	48,888		$	46,249
Service Cost		2,399			2,308			1,089			1,099
Interest Cost		3,143			3,046			1,964			1,952
Actuarial Loss		6,203			2,810			3,052			141
Benefits Paid		(2,333	)		(2,105	)		(648	)		(553	)
Ending Balance	$	88,013		$	78,601		$	54,345		$	48,888

	December 31,
	2017			2016			2017			2016
Change in Fair Value of Plan Assets:
Beginning Balance	$	59,370		$	52,931		$	31,607		$	29,018
Actual Return on Plan Assets		8,543			4,909			3,521			1,591
Employer Contributions		3,635			3,635			1,603			1,551
Benefits Paid		(2,333	)		(2,105	)		(648	)		(553	)
Ending Balance	$	69,215		$	59,370		$	36,083		$	31,607

Funded Status	$	(18,798	)	$	(19,231	)	$	(18,262	)	$	(17,281	)

	(Thousands of Dollars)
	Pension Plan				Other Benefits Plan
	December 31,
	2017		2016		2017		2016
Amounts Recognized in the Consolidated Balance Sheets consist of :
Current Liability		374		373		—		—
Noncurrent Liability		18,424		18,858		18,262		17,281
Net Liability Recognized	$	18,798	$	19,231	$	18,262	$	17,281

	(Thousands of Dollars)
	Pension Plan									Other Benefits Plan
	Years Ended December 31,
	2017			2016			2015			2017			2016			2015
Components of Net Periodic Benefit Cost
Service Cost	$	2,399		$	2,308		$	2,558		$	1,089		$	1,099		$	1,373
Interest Cost		3,143			3,046			2,894			1,964			1,952			1,921
Expected Return on Plan Assets		(4,489	)		(4,014	)		(3,919	)		(2,406	)		(2,213	)		(2,107	)
Amortization of Net Actuarial Loss		1,566			1,426			1,645			1,781			1,773			2,261
Amortization of Prior Service Credit		—			—			—			(1,728	)		(1,728	)		(1,728	)
Net Periodic Benefit Cost	$	2,619		$	2,766		$	3,178		$	700		$	883		$	1,720

Amounts that are expected to be amortized from Regulatory Assets into Net Periodic Benefit Cost in 2018 are as follows:

	(Thousands of Dollars)
	Pension Plan		Other Benefits Plan
Actuarial Loss	$	1,658	$	1,787
Prior Service Credit		—		(1,607	)

The discount rate and compensation increase rate for determining our postretirement benefit plans’ benefit obligations and costs as of and for the years ended December 31, 2017, 2016 and 2015, respectively, are as follows:

	Pension Plan			Other Benefits Plan
	2017	2016	2015	2017	2016	2015
Weighted Average Assumptions:
Expected Return on Plan Assets	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%
Discount Rate for:
Benefit Obligation	3.53%	4.06%	4.26%	3.53%	4.06%	4.26%
Benefit Cost	4.06%	4.26%	3.91%	4.06%	4.26%	3.91%
Compensation Increase for:
Benefit Obligation	3.00%	3.00%	3.00%	3.00%	3.00%	3.00%
Benefit Cost	3.00%	3.00%	3.00%	3.00%	3.00%	3.00%

The compensation increase assumption for the Other Benefits Plan is attributable to life insurance provided to qualifying employees upon their retirement. The insurance coverage will be determined based on the employee’s base compensation as of their retirement date.

The Company utilizes the Society of Actuaries’ mortality table (RP 2014) (Mortality Improvement Scale MP2017 for the 2017 valuation).

For the 2017 valuation, costs and obligations for our Other Benefits Plan assumed a 9.0% annual rate of increase in the per capita cost of covered healthcare benefits in 2018 with the annual rate of increase declining 1.0% per year for 2019-2021 and 0.5% per year for 2022-2023, resulting in an annual rate of increase in the per capita cost of covered healthcare benefits of 5% by year 2023.

A one-percentage point change in assumed healthcare cost trend rates would have the following effects on the Other Benefits Plan:

	(Thousands of Dollars)
	1 Percentage Point
	Increase		Decrease
Effect on Current Year Service and Interest Costs	$	649	$	(499	)
Effect on Projected Benefit Obligation	$	9,412	$	(7,403	)

The following benefit payments, which reflect expected future service, are expected to be paid:

	(Thousands of Dollars)
Year	Pension Plan		Other Benefits Plan
2018	$	2,639	$	1,174
2019		2,653		1,414
2020		2,875		1,614
2021		2,971		1,816
2022		3,360		2,027
2023-2027		23,789		11,674
Totals	$	38,287	$	19,719

Benefit Plans Assets

The allocation of plan assets at December 31, 2017 and 2016 by asset category is as follows:

	Pension Plan						Other Benefits Plan
Asset Category	2017		2016		Target		2017		2016		Target
Equity Securities		62.8%		59.7%		55%		57.7%		54.1%		43%
Debt Securities		33.6%		36.6%		38%		32.9%		43.3%		50%
Cash		1.0%		1.0%		2%		9.4%		2.6%		2%
Real Estate/Commodities		2.6%		2.7%		5%		0.0%		0.0%		5%
Total		100.0%		100.0%				100.0%		100.0%

Two outside investment firms each manage a portion of the Pension Plan asset portfolio. One of those investment firms also manages the Other Benefits Plan asset portfolio. Quarterly meetings are held between the Company’s Pension Committee of the Board of Directors and the investment managers to review their performance and asset allocation. If the actual asset allocation is outside the targeted range, the Pension Committee reviews current market conditions and advice provided by the investment managers to determine the appropriateness of rebalancing the portfolio.

The objective of the Company is to maximize the long-term return on retirement plan assets, relative to a reasonable level of risk, maintain a diversified investment portfolio and maintain compliance with the Employee Retirement Income Security Act of 1974. The expected long-term rate of return is based on the various asset categories in which plan assets are invested and the current expectations and historical performance for these categories.

Equity securities include Middlesex common stock in the amounts of $0.8 million (1.1% of total Pension Plan assets) and $0.8 million (1.4% of total Pension Plan assets) and as of December 31, 2017 and 2016, respectively.

Fair Value Measurements

Accounting guidance provides a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurements) and the lowest priority to unobservable inputs (Level 3 measurements). The three levels of the fair value hierarchy are described as follows:

Level 1 – Inputs to the valuation methodology are unadjusted quoted market prices for identical assets or liabilities in accessible active markets.

Level 2 – Inputs to the valuation methodology that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. If the asset or liability has a specified contractual term, the Level 2 input must be observable for substantially the full term of the asset or liability.

Level 3 – Inputs to the valuation methodology are unobservable and significant to the fair value measurement.

Certain investments in cash and cash equivalents, equity securities, and commodities are valued based on quoted market prices in active markets and are classified as Level 1 investments. Certain investments in cash and cash equivalents, equity securities and fixed income securities are valued using prices received from pricing vendors that utilize observable inputs and are therefore classified as Level 2 investments.

The following tables present Middlesex’s Pension Plan assets measured and recorded at fair value within the fair value hierarchy:

	(Thousands of Dollars)
	As of December 31, 2017
	Level 1		Level 2		Level 3		Total
Mutual Funds	$	57,608	$	—	$	—	$	57,608
Money Market Funds		677		—		—		677
Common Equity Securities		10,930		—		—		10,930
Total Investments	$	69,215	$	—	$	—	$	69,215

	(Thousands of Dollars)
	As of December 31, 2016
	Level 1		Level 2		Level 3		Total
Mutual Funds	$	49,439	$	—	$	—	$	49,439
Money Market Funds		648		—		—		648
Common Equity Securities		9,283		—		—		9,283
Total Investments	$	59,370	$	—	$	—	$	59,370

The following tables present Middlesex’s Other Benefits Plan assets measured and recorded at fair value within the fair value hierarchy:

	(Thousands of Dollars)
	As of December 31, 2017
	Level 1		Level 2		Level 3		Total

Mutual Funds	$	20,819	$	—	$	—	$	20,819
Money Market Funds		3,388		—		—		3,388
Preferred Equity Securities		115		—		—		115
Agency/US/State/Municipal Debt		—		11,761		—		11,761
Total Investments	$	24,322	$	11,761	$	—	$	36,083

	(Thousands of Dollars)
	As of December 31, 2016
	Level 1		Level 2		Level 3		Total
Mutual Funds	$	17,096	$	—	$	—	$	17,096
Money Markey Funds		826		—		—		826
Preferred Equity Securities		108		—		—		108
Agency/US/State/Municipal Debt		—		13,577		—		13,577
Total Investments	$	18,030	$	13,577	$	—	$	31,607

Benefit Plans Contributions

For the Pension Plan, Middlesex made total cash contributions of $3.6 million in 2017 and expects to make approximately $3.3 million of cash contributions in 2018.

For the Other Benefits Plan, Middlesex made total cash contributions of $1.6 million in 2017 and expects to make approximately $1.6 million of cash contributions in 2018.

401(k) Plan

The Company maintains a 401(k) defined contribution plan, which covers substantially all employees with more than 1,000 hours of service. Under the terms of the Plan, the Company matches 100% of a participant’s contributions, which do not exceed 1% of a participant’s compensation, plus 50% of a participant’s contributions exceeding 1%, but not more than 6%. The Company’s matching contribution was $0.6 million for each of the years ended December 31, 2017, 2016 and 2015.

For those employees hired after March 31, 2007, and still actively employed on December 31, 2017, the Company approved, and will fund, a discretionary contribution of $0.5 million which was based on 5.0% of eligible 2017 compensation. For each of the years ended December 31, 2016 and 2015, the Company made discretionary contributions of $0.4 million for qualifying employees.

Stock-Based Compensation

The Company has a stock compensation plan for certain management employees (the 2008 Restricted Stock Plan). The Company maintains an escrow account for 0.1 million shares of the Company's common stock for the 2008 Restricted Stock Plan. Shares issued in connection with the 2008 Restricted Stock Plan are subject to forfeiture by the employee in the event of termination of employment within five years of the award other than as a result of normal retirement, death, disability or change in control. The maximum number of shares authorized for grant under the 2008 Restricted Stock Plan is 0.3 million shares, for which less than 50,000 shares remain as unissued shares. The 2008 Restricted Stock Plan terminates on March 31, 2018.

The Company recognizes compensation expense at fair value for the 2008 Restricted Stock Plan awards in accordance with ASC 718, Compensation – Stock Compensation. Compensation expense is determined by the market value of the stock on the date of the award and is being amortized over a five-year period.

The following table presents information on the 2008 Restricted Stock Plan:

	Shares (thousands)			Unearned Compensation (thousands)			Weighted Average Grant Price
Balance, January 1, 2015		127		$	1,483
Granted		33			741		$	22.65
Vested		(12	)		—
Forfeited		—			—
Amortization of Compensation Expense		—			(528	)
Balance, December 31, 2015		148		$	1,696
Granted		24			750		$	30.85
Vested		(25	)		—
Forfeited		—			—
Amortization of Compensation Expense		—			(682	)
Balance, December 31, 2016		147		$	1,764
Granted		22			799		$	36.95
Vested		(20	)		—
Forfeited		(2	)		(54	)
Amortization of Compensation Expense		—			(724	)
Balance, December 31, 2017		147		$	1,785

The fair value of vested restricted shares was $0.8 million and $0.9 million as of December 31, 2017 and 2016, respectively.

Business Segment Data

12 Months Ended

Dec. 31, 2017

Segment Reporting [Abstract]

Business Segment Data

Note 8 – Business Segment Data

The Company has identified two reportable segments. One is the regulated business of collecting, treating and distributing water on a retail and wholesale basis to residential, commercial, industrial and fire protection customers in parts of New Jersey, Delaware and Pennsylvania. This segment also includes regulated wastewater systems in New Jersey and Delaware. The Company is subject to regulations as to its rates, services and other matters by the states of New Jersey, Delaware and Pennsylvania with respect to utility service within these states. The other segment is primarily comprised of non-regulated contract services for the operation and maintenance of municipal and private water and wastewater systems in New Jersey and Delaware.

Inter-segment transactions relating to operational costs are treated as pass-through expenses. Finance charges on inter-segment loan activities are based on interest rates that are below what would normally be charged by a third party lender.

	(Thousands of Dollars)
	Years Ended December 31,
Operations by Segments:	2017			2016			2015
Revenues:
Regulated	$	115,454		$	118,017		$	111,247
Non – Regulated		15,912			15,388			15,238
Inter-segment Elimination		(591	)		(499	)		(460	)
Consolidated Revenues	$	130,775		$	132,906		$	126,025

Operating Income:
Regulated	$	35,952		$	38,201		$	33,603
Non – Regulated		2,668			2,431			2,237
Consolidated Operating Income	$	38,620		$	40,632		$	35,840

Depreciation:
Regulated	$	13,732		$	12,606		$	11,874
Non – Regulated		190			190			177
Consolidated Depreciation	$	13,922		$	12,796		$	12,051

Other Income (Expense), Net:
Regulated	$	1,198		$	779		$	619
Non – Regulated		64			(1,308	)		20
Inter-segment Elimination		(467	)		(333	)		(346	)
Consolidated Other Income (Expense), Net	$	795		$	(862	)	$	293

Interest Expense:
Regulated	$	5,855		$	5,293		$	5,554
Non – Regulated		118			89			89
Inter-segment Elimination		(467	)		(89	)		(89	)
Consolidated Interest Charges	$	5,506		$	5,293		$	5,554

Income Taxes:
Regulated	$	9,848		$	11,091		$	9,522
Non – Regulated		1,252			644			1,029
Consolidated Income Taxes	$	11,100		$	11,735		$	10,551

Net Income:
Regulated	$	21,447		$	22,353		$	18,889
Non – Regulated		1,362			389			1,139
Consolidated Net Income	$	22,809		$	22,742		$	20,028

Capital Expenditures:
Regulated	$	50,078		$	47,189		$	25,706
Non – Regulated		223			186			67
Total Capital Expenditures	$	50,301		$	47,375			$ 25, 773

	(Thousands of Dollars)
	As of December 31, 2017			As of December 31, 2016
Assets:
Regulated	$	661,816		$	619,915
Non – Regulated		7,093			6,245
Inter-segment Elimination		(7,769	)		(5,999	)
Consolidated Assets	$	661,140		$	620,161

Quarterly Operating Results - Unaudited

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Quarterly Operating Results - Unaudited

Note 9 - Quarterly Operating Results - Unaudited

Operating results for each quarter of 2017 and 2016 are as follows:

	(Thousands of Dollars, Except per Share Data)
2017	1^st		2^nd		3^rd		4^th		Total

Operating Revenues	$	30, 131	$	33,014	$	36,174	$	31, 456	$	130,775
Operating Income		7,780		9,563		12,806		8,471		38,620
Net Income		4,441		5,381		7,642		5,345		22,809
Basic Earnings per Share	$	0.27	$	0.33	$	0.47	$	0.32	$	1.39
Diluted Earnings per Share	$	0.27	$	0.33	$	0.46	$	0.32	$	1.38

2016	1^st		2^nd		3^rd		4^th		Total

Operating Revenues	$	30,579	$	32,725	$	37,754	$	31,808	$	132,906
Operating Income		8,302		10,328		14,156		7,846		40,632
Net Income		4,790		5,919		8,813		3,220		22,742
Basic Earnings per Share	$	0.29	$	0.36	$	0.54	$	0.20	$	1.39
Diluted Earnings per Share	$	0.29	$	0.36	$	0.54	$	0.19	$	1.38

The information above, in the opinion of the Company, includes all adjustments consisting only of normal recurring accruals necessary for a fair presentation of such amounts. The business of the Company is subject to seasonal fluctuation with the peak period usually occurring during the summer months. The quarterly earnings per share amounts above may differ from previous filings due to the effects of rounding.

Organization, Summary of Significant Accounting Policies and Recent Developments (Policies)

12 Months Ended

Dec. 31, 2017

Organization Summary Of Significant Accounting Policies And Recent Developments [Abstract]

Organization

Principles of Consolidation

System of Accounts

Regulatory Accounting

Retirement Benefit Plans

Utility Plant

Depreciation

Source of Supply	1.15% - 3.44%	Transmission and Distribution (T&D):
Pumping	2.00% - 5.39%	T&D – Mains	1.10% - 3.13%
Water Treatment	1.65% - 7.09%	T&D – Services	2.12% - 3.16%
General Plant	2.08% - 17.84%	T&D – Other	1.61% - 4.63%
Wastewater Collection	1.42% - 1.81%

Preliminary Survey and Investigation (PS&I) Costs

Customers' Advances for Construction (CAC)

Contributions in Aid of Construction (CIAC)

Contributions in Aid of Construction (CIAC) – CIAC include direct non-refundable contributions of utility plant and/or cash and the portion of CAC that becomes non-refundable.

CAC and CIAC are not depreciated in accordance with regulatory requirements. In addition, these amounts reduce the investment base for purposes of setting rates.

Allowance for Funds Used During Construction (AFUDC)

	2017	2016	2015
Middlesex	6.73%	6.73%	6.72%
Tidewater	7.92%	7.92%	7.92%

Accounts Receivable

Revenues

Southern Shores is an unmetered system. Customers are billed a fixed service charge in advance at the beginning of each month and revenues are recognized as earned.

Customers in portions of the TESI system are billed a fixed service charge in arrears.

Unamortized Debt Expense and Premiums on Long-Term Debt

Income Taxes

Statements of Cash Flows

Restricted Cash

Use of Estimates

Recent Accounting Pronouncements

(r) Recent Accounting Pronouncements

There are no other new adopted or proposed accounting guidance that the Company is aware of that could have a material impact on the Company’s financial statements.

Organization, Summary of Significant Accounting Policies and Recent Developments (Tables)

12 Months Ended

Dec. 31, 2017

Organization Summary Of Significant Accounting Policies And Recent Developments [Abstract]

Range of depreciation rates

The following table sets forth the range of depreciation rates for the major utility plant categories used to calculate depreciation for the years ended December 31, 2017, 2016 and 2015. These rates have been approved by the NJBPU, DEPSC or PAPUC:

Source of Supply	1.15% - 3.44%	Transmission and Distribution (T&D):
Pumping	2.00% - 5.39%	T&D – Mains	1.10% - 3.13%
Water Treatment	1.65% - 7.09%	T&D – Services	2.12% - 3.16%
General Plant	2.08% - 17.84%	T&D – Other	1.61% - 4.63%
Wastewater Collection	1.42% - 1.81%

Allowance for Funds Used During Construction Rates

The AFUDC rates for the years ended December 31, 2017, 2016 and 2015 for Middlesex and Tidewater are as follows:

	2017	2016	2015
Middlesex	6.73%	6.73%	6.72%
Tidewater	7.92%	7.92%	7.92%

Rate and Regulatory Matters (Tables)

12 Months Ended

Dec. 31, 2017

Regulated Operations [Abstract]

Schedule of regulatory assets

	(Thousands of Dollars)
	December 31,				Remaining
Regulatory Assets	2017		2016		Recovery Periods
Retirement Benefits	$	43,070	$	40,603	Various
Income Taxes		9,876		15,899	Various
Rate Cases, Tank Painting, and Other		5,477		4,392	2-10 years
Total	$	58,423	$	60,894

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Income tax expense reconciliation

Income tax expense differs from the amount computed by applying the statutory rate on book income subject to tax for the following reasons:

	(Thousands of Dollars)
	Years Ended December 31,
	2017			2016			2015
Income Tax at Statutory Rate	$	11,868		$	12,007		$	10,703
Tax Effect of:
Utility Plant Related		(1,016	)		(1,059	)		(920	)
State Income Taxes – Net		895			770			745
Tax Act		(610	)		—			—
Employee Benefits		(43	)		(5	)		7
Other		6			22			16
Total Income Tax Expense	$	11,100		$	11,735		$	10,551

Income tax expense

Income tax expense is comprised of the following:

	(Thousands of Dollars)
	Years Ended December 31,
	2017			2016			2015
Current:
Federal	$	2,090		$	7,305		$	(15,203	)
State		1,066			877			1,153
Deferred:
Federal		7,713			3,325			24,686
State		310			307			(6	)
Investment Tax Credits		(79	)		(79	)		(79	)
Total Income Tax Expense	$	11,100		$	11,735		$	10,551

Deferred tax liability

	(Thousands of Dollars)
	December 31,
	2017			2016
Utility Plant Related	$	41,259		$	69,019
Customer Advances		(3,749	)		(3,430	)
Employee Benefits		4,903			6,904
Investment Tax Credits (ITC)		675			753
Other		72			(421	)
Total Deferred Tax Liability and ITC	$	43,160		$	72,825

Commitments and Contingent Liabilities (Tables)

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies Disclosure [Abstract]

Schedule of water cost purchased

Purchased water costs are shown below:

	(Millions of Dollars)
	Years Ended December 31,
Purchased Water	2017		2016		2015
Untreated	$	2.8	$	2.6	$	2.5
Treated		3.3		3.2		3.1
Total Costs	$	6.1	$	5.8	$	5.6

Schedule of future minimum operating lease

The minimum annual future rental commitment under operating leases that have initial or remaining non-cancelable lease terms over the next 5 years and thereafter are as follows:

Year	(Millions of Dollars) Annual Maturities
2018	$ 0.7
2019	$ 0.7
2020	$ 0.7
2021	$ 0.7
2022	$ 0.7
Thereafter	$ 3.8

Short-Term Borrowings (Tables)

12 Months Ended

Dec. 31, 2017

Short-term Debt [Abstract]

Schedule of information regarding short-term borrowings

Information regarding the Company’s short-term borrowings for the years ended December 31, 2017 and 2016 is summarized below:

	(Millions of Dollars)
	2017			2016
Established Lines at Year-End	$	92.0		$	60.0
Maximum Amount Outstanding		28.0			13.1
Average Outstanding		18.6			7.4
Notes Payable at Year-End		28.0			12.0
Weighted Average Interest Rate		2.15	%		1.54	%
Weighted Average Interest Rate at Year-End		2.54	%		1.71	%

Capitalization (Tables)

12 Months Ended

Dec. 31, 2017

CAPITALIZATION:

Schedule of maturities of long term debt

The aggregate annual principal repayment obligations for all long-term debt over the next five years are shown below:

Year	(Millions of Dollars) Annual Maturities
2018	$ 6.9
2019	$ 7.1
2020	$ 6.9
2021	$ 6.9
2022	$ 6.4

Schedule of earnings per share

	(In Thousands, Except Per Share Amounts)
	2017					2016					2015
Basic:	Income			Shares		Income			Shares		Income			Shares
Net Income	$	22,809			16,330	$	22,742			16,270	$	20,028			16,175
Preferred Dividend		(144	)				(144	)				(144	)
Earnings Applicable to Common Stock	$	22,665			16,330	$	22,598			16,270	$	19,884			16,175
Basic EPS	$	1.39				$	1.39				$	1.23
Diluted:
Earnings Applicable to Common Stock	$	22,665			16,330	$	22,598			16,270	$	19,884			16,175
$7.00 Series Dividend		67			115		67			115		67			115
$8.00 Series Dividend		24			41		24			41		24			41
Adjusted Earnings Applicable to Common Stock	$	22,756			16,486	$	22,689			16,426	$	19,975			16,331
Diluted EPS	$	1.38				$	1.38				$	1.22

Schedule of carrying amount and estimated fair value of bonds

	(Thousands of Dollars)
	At December 31,
	2017				2016
	Carrying		Fair		Carrying		Fair
	Amount		Value		Amount		Value
Bonds	$	95,322	$	98,036	$	82,786	$	84,821

Employee Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2017

Retirement Benefits [Abstract]

Change in projected benefit obligation and fair value of plan assets

	(Thousands of Dollars)
	Pension Plan						Other Benefits Plan
	December 31,
	2017			2016			2017			2016
Change in Projected Benefit Obligation:
Beginning Balance	$	78,601		$	72,542		$	48,888		$	46,249
Service Cost		2,399			2,308			1,089			1,099
Interest Cost		3,143			3,046			1,964			1,952
Actuarial Loss		6,203			2,810			3,052			141
Benefits Paid		(2,333	)		(2,105	)		(648	)		(553	)
Ending Balance	$	88,013		$	78,601		$	54,345		$	48,888

	December 31,
	2017			2016			2017			2016
Change in Fair Value of Plan Assets:
Beginning Balance	$	59,370		$	52,931		$	31,607		$	29,018
Actual Return on Plan Assets		8,543			4,909			3,521			1,591
Employer Contributions		3,635			3,635			1,603			1,551
Benefits Paid		(2,333	)		(2,105	)		(648	)		(553	)
Ending Balance	$	69,215		$	59,370		$	36,083		$	31,607

Funded Status	$	(18,798	)	$	(19,231	)	$	(18,262	)	$	(17,281	)

Amounts recognized in balance sheet

	(Thousands of Dollars)
	Pension Plan				Other Benefits Plan
	December 31,
	2017		2016		2017		2016
Amounts Recognized in the Consolidated Balance Sheets consist of :
Current Liability		374		373		—		—
Noncurrent Liability		18,424		18,858		18,262		17,281
Net Liability Recognized	$	18,798	$	19,231	$	18,262	$	17,281

Components of net benefit cost

	(Thousands of Dollars)
	Pension Plan									Other Benefits Plan
	Years Ended December 31,
	2017			2016			2015			2017			2016			2015
Components of Net Periodic Benefit Cost
Service Cost	$	2,399		$	2,308		$	2,558		$	1,089		$	1,099		$	1,373
Interest Cost		3,143			3,046			2,894			1,964			1,952			1,921
Expected Return on Plan Assets		(4,489	)		(4,014	)		(3,919	)		(2,406	)		(2,213	)		(2,107	)
Amortization of Net Actuarial Loss		1,566			1,426			1,645			1,781			1,773			2,261
Amortization of Prior Service Credit		—			—			—			(1,728	)		(1,728	)		(1,728	)
Net Periodic Benefit Cost	$	2,619		$	2,766		$	3,178		$	700		$	883		$	1,720

Amounts expected to be amortized from regulatory assets

Amounts that are expected to be amortized from Regulatory Assets into Net Periodic Benefit Cost in 2018 are as follows:

	(Thousands of Dollars)
	Pension Plan		Other Benefits Plan
Actuarial Loss	$	1,658	$	1,787
Prior Service Credit		—		(1,607	)

Discount and compensation rates

	Pension Plan			Other Benefits Plan
	2017	2016	2015	2017	2016	2015
Weighted Average Assumptions:
Expected Return on Plan Assets	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%
Discount Rate for:
Benefit Obligation	3.53%	4.06%	4.26%	3.53%	4.06%	4.26%
Benefit Cost	4.06%	4.26%	3.91%	4.06%	4.26%	3.91%
Compensation Increase for:
Benefit Obligation	3.00%	3.00%	3.00%	3.00%	3.00%	3.00%
Benefit Cost	3.00%	3.00%	3.00%	3.00%	3.00%	3.00%

Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates

A one-percentage point change in assumed healthcare cost trend rates would have the following effects on the Other Benefits Plan:

	(Thousands of Dollars)
	1 Percentage Point
	Increase		Decrease
Effect on Current Year Service and Interest Costs	$	649	$	(499	)
Effect on Projected Benefit Obligation	$	9,412	$	(7,403	)

Expected benefit payments

The following benefit payments, which reflect expected future service, are expected to be paid:

	(Thousands of Dollars)
Year	Pension Plan		Other Benefits Plan
2018	$	2,639	$	1,174
2019		2,653		1,414
2020		2,875		1,614
2021		2,971		1,816
2022		3,360		2,027
2023-2027		23,789		11,674
Totals	$	38,287	$	19,719

Allocation of plan assets

The allocation of plan assets at December 31, 2017 and 2016 by asset category is as follows:

	Pension Plan						Other Benefits Plan
Asset Category	2017		2016		Target		2017		2016		Target
Equity Securities		62.8%		59.7%		55%		57.7%		54.1%		43%
Debt Securities		33.6%		36.6%		38%		32.9%		43.3%		50%
Cash		1.0%		1.0%		2%		9.4%		2.6%		2%
Real Estate/Commodities		2.6%		2.7%		5%		0.0%		0.0%		5%
Total		100.0%		100.0%				100.0%		100.0%

Fair value of plan assets

The following tables present Middlesex’s Pension Plan assets measured and recorded at fair value within the fair value hierarchy:

	(Thousands of Dollars)
	As of December 31, 2017
	Level 1		Level 2		Level 3		Total
Mutual Funds	$	57,608	$	—	$	—	$	57,608
Money Market Funds		677		—		—		677
Common Equity Securities		10,930		—		—		10,930
Total Investments	$	69,215	$	—	$	—	$	69,215

	(Thousands of Dollars)
	As of December 31, 2016
	Level 1		Level 2		Level 3		Total
Mutual Funds	$	49,439	$	—	$	—	$	49,439
Money Market Funds		648		—		—		648
Common Equity Securities		9,283		—		—		9,283
Total Investments	$	59,370	$	—	$	—	$	59,370

The following tables present Middlesex’s Other Benefits Plan assets measured and recorded at fair value within the fair value hierarchy:

	(Thousands of Dollars)
	As of December 31, 2017
	Level 1		Level 2		Level 3		Total

Mutual Funds	$	20,819	$	—	$	—	$	20,819
Money Market Funds		3,388		—		—		3,388
Preferred Equity Securities		115		—		—		115
Agency/US/State/Municipal Debt		—		11,761		—		11,761
Total Investments	$	24,322	$	11,761	$	—	$	36,083

	(Thousands of Dollars)
	As of December 31, 2016
	Level 1		Level 2		Level 3		Total
Mutual Funds	$	17,096	$	—	$	—	$	17,096
Money Markey Funds		826		—		—		826
Preferred Equity Securities		108		—		—		108
Agency/US/State/Municipal Debt		—		13,577		—		13,577
Total Investments	$	18,030	$	13,577	$	—	$	31,607

Restricted stock plan

The following table presents information on the 2008 Restricted Stock Plan:

	Shares (thousands)			Unearned Compensation (thousands)			Weighted Average Grant Price
Balance, January 1, 2015		127		$	1,483
Granted		33			741		$	22.65
Vested		(12	)		—
Forfeited		—			—
Amortization of Compensation Expense		—			(528	)
Balance, December 31, 2015		148		$	1,696
Granted		24			750		$	30.85
Vested		(25	)		—
Forfeited		—			—
Amortization of Compensation Expense		—			(682	)
Balance, December 31, 2016		147		$	1,764
Granted		22			799		$	36.95
Vested		(20	)		—
Forfeited		(2	)		(54	)
Amortization of Compensation Expense		—			(724	)
Balance, December 31, 2017		147		$	1,785

Business Segment Data (Tables)

12 Months Ended

Dec. 31, 2017

Segment Reporting [Abstract]

Schedule of Segment Reporting Information, by Segment

	(Thousands of Dollars)
	Years Ended December 31,
Operations by Segments:	2017			2016			2015
Revenues:
Regulated	$	115,454		$	118,017		$	111,247
Non – Regulated		15,912			15,388			15,238
Inter-segment Elimination		(591	)		(499	)		(460	)
Consolidated Revenues	$	130,775		$	132,906		$	126,025

Operating Income:
Regulated	$	35,952		$	38,201		$	33,603
Non – Regulated		2,668			2,431			2,237
Consolidated Operating Income	$	38,620		$	40,632		$	35,840

Depreciation:
Regulated	$	13,732		$	12,606		$	11,874
Non – Regulated		190			190			177
Consolidated Depreciation	$	13,922		$	12,796		$	12,051

Other Income (Expense), Net:
Regulated	$	1,198		$	779		$	619
Non – Regulated		64			(1,308	)		20
Inter-segment Elimination		(467	)		(333	)		(346	)
Consolidated Other Income (Expense), Net	$	795		$	(862	)	$	293

Interest Expense:
Regulated	$	5,855		$	5,293		$	5,554
Non – Regulated		118			89			89
Inter-segment Elimination		(467	)		(89	)		(89	)
Consolidated Interest Charges	$	5,506		$	5,293		$	5,554

Income Taxes:
Regulated	$	9,848		$	11,091		$	9,522
Non – Regulated		1,252			644			1,029
Consolidated Income Taxes	$	11,100		$	11,735		$	10,551

Net Income:
Regulated	$	21,447		$	22,353		$	18,889
Non – Regulated		1,362			389			1,139
Consolidated Net Income	$	22,809		$	22,742		$	20,028

Capital Expenditures:
Regulated	$	50,078		$	47,189		$	25,706
Non – Regulated		223			186			67
Total Capital Expenditures	$	50,301		$	47,375			$ 25, 773

	(Thousands of Dollars)
	As of December 31, 2017			As of December 31, 2016
Assets:
Regulated	$	661,816		$	619,915
Non – Regulated		7,093			6,245
Inter-segment Elimination		(7,769	)		(5,999	)
Consolidated Assets	$	661,140		$	620,161

Quarterly Operating Results - Unaudited (Tables)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Quarterly financial information

Operating results for each quarter of 2017 and 2016 are as follows:

	(Thousands of Dollars, Except per Share Data)
2017	1^st		2^nd		3^rd		4^th		Total

Operating Revenues	$	30, 131	$	33,014	$	36,174	$	31, 456	$	130,775
Operating Income		7,780		9,563		12,806		8,471		38,620
Net Income		4,441		5,381		7,642		5,345		22,809
Basic Earnings per Share	$	0.27	$	0.33	$	0.47	$	0.32	$	1.39
Diluted Earnings per Share	$	0.27	$	0.33	$	0.46	$	0.32	$	1.38

2016	1^st		2^nd		3^rd		4^th		Total

Operating Revenues	$	30,579	$	32,725	$	37,754	$	31,808	$	132,906
Operating Income		8,302		10,328		14,156		7,846		40,632
Net Income		4,790		5,919		8,813		3,220		22,742
Basic Earnings per Share	$	0.29	$	0.36	$	0.54	$	0.20	$	1.39
Diluted Earnings per Share	$	0.29	$	0.36	$	0.54	$	0.19	$	1.38

Organization, Summary of Significant Accounting Policies and Recent Developments (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Organization, Summary Of Significant Accounting Policies And Recent Developments [Line Items]
Percent voting interest	50.00%
Percent of operating revenues	88.00%
Percent of total assets	99.00%
Allowance for doubtful accounts	$ 900	$ 900
Bad debt expense	500	700	$ 800
Write-offs	500	$ 600	$ 600
Investment	200
Loan to RGRME	1,700
Uncollectible notes receivable	1,700
Noncash impairment charge	$ 200
Minimum [Member]
Organization, Summary Of Significant Accounting Policies And Recent Developments [Line Items]
Estimated useful lives of non-regulated fixed assets	3 years
Maximum [Member]
Organization, Summary Of Significant Accounting Policies And Recent Developments [Line Items]
Estimated useful lives of non-regulated fixed assets	40 years

Organization, Summary of Significant Accounting Policies and Recent Developments (Schedule of Depreciation Rates) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Source of Supply [Member] \| Minimum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	1.15%	1.15%	1.15%
Source of Supply [Member] \| Maximum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	3.44%	3.44%	3.44%
Pumping [Member] \| Minimum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	2.00%	2.00%	2.00%
Pumping [Member] \| Maximum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	5.39%	5.39%	5.39%
Water Treatment [Member] \| Minimum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	1.65%	1.65%	1.65%
Water Treatment [Member] \| Maximum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	7.09%	7.09%	7.09%
General Plant [Member] \| Minimum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	2.08%	2.08%	2.08%
General Plant [Member] \| Maximum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	17.84%	17.84%	17.84%
Wastewater Collection [Member] \| Minimum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	1.42%	1.42%	1.42%
Wastewater Collection [Member] \| Maximum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	1.81%	1.81%	1.81%
T&D Mains [Member] \| Minimum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	1.10%	1.10%	1.10%
T&D Mains [Member] \| Maximum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	3.13%	3.13%	3.13%
T&D Services [Member] \| Minimum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	2.12%	2.12%	2.12%
T&D Services [Member] \| Maximum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	3.16%	3.16%	3.16%
T&D Other [Member] \| Minimum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	1.61%	1.61%	1.61%
T&D Other [Member] \| Maximum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	4.63%	4.63%	4.63%

Organization, Summary of Significant Accounting Policies and Recent Developments (Schedule of AFUDC Rates) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Middlesex [Member]
Organization, Summary Of Significant Accounting Policies And Recent Developments [Line Items]
Allowance for Funds Used During Construction Rates	6.73%	6.73%	6.72%
Tidewater [Member]
Organization, Summary Of Significant Accounting Policies And Recent Developments [Line Items]
Allowance for Funds Used During Construction Rates	7.92%	7.92%	7.92%

Rate and Regulatory Matters (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended				12 Months Ended
	Oct. 31, 2017	Jun. 30, 2016	Apr. 30, 2016	Aug. 31, 2015	Dec. 31, 2017	Dec. 31, 2016
Regulatory Liabilities [Line Items]
Regulatory Liability - Cost of Utility Plant Removal					$ 43,745	$ 11,337
Acquisition premiums to be recovered					$ 500
Percentage of corporate tax regulated compaines pre-tax					92.00%
Regulatory liabilities					$ 31,600
Decrease in Regulatory assets					5,900
Middlesex [Member] \| New Jersey Board Of Public Utilities [Member]
Regulatory Liabilities [Line Items]
Additional annual costs	$ 1,200
Base rate amount	$ 15,300			$ 219,000
Return on equity				9.75%
Increase in base rates revenue per year				$ 5,000
Tidewater [Member] \| Delaware Public Service Commission [Member]
Regulatory Liabilities [Line Items]
Approved increase in annual operating revenues					400
Pinelands Water Company [Member]
Regulatory Liabilities [Line Items]
Approved increase in annual operating revenues			$ 200
Pinelands Wastewater [Member]
Regulatory Liabilities [Line Items]
Approved increase in annual operating revenues			$ 100
Southern Shores [Member] \| Delaware Public Service Commission [Member]
Regulatory Liabilities [Line Items]
Originally filed increase in annual operating revenue					$ 100
Twin Lakes [Member]
Regulatory Liabilities [Line Items]
Approved increase in annual operating revenues		$ 100
Maximum [Member]
Regulatory Liabilities [Line Items]
Corporate tax rate					35.00%
Minimum [Member]
Regulatory Liabilities [Line Items]
Corporate tax rate					21.00%

Rate and Regulatory Matters (Schedule of Regulatory Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Regulatory Assets [Line Items]
Regulatory Assets	$ 58,423	$ 60,894
Retirement Benefits [Member]
Regulatory Assets [Line Items]
Regulatory Assets	$ 43,070	$ 40,603
Remaining recovery period	<div id='EdgarSAA123457890000' style="font-family : 'Times New Roman';">Various</div>	<div id='EdgarSAA123457890000' style="font-family : 'Times New Roman';">Various</div>
Income Taxes [Member]
Regulatory Assets [Line Items]
Regulatory Assets	$ 9,876	$ 15,899
Remaining recovery period	<div id='EdgarSAA123457890000' style="font-family : 'Times New Roman';">Various</div>	<div id='EdgarSAA123457890000' style="font-family : 'Times New Roman';">Various</div>
Rate Cases, Tank Painting, and Other [Member]
Regulatory Assets [Line Items]
Regulatory Assets	$ 5,477	$ 4,392
Remaining recovery period	2-10 years	2-10 years

Income Taxes (Schedule of Income Tax Expense Reconciliation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income Tax at Statutory Rate	$ 11,868	$ 12,007	$ 10,703
Tax Effect of:
Utility Plant Related	(1,016)	(1,059)	(920)
State Income Taxes - Net	895	770	745
Tax Act	(610)
Employee Benefits	(43)	(5)	7
Other	6	22	16
Total Income Tax Expense	$ 11,100	$ 11,735	$ 10,551

Income Taxes (Schedule of Income Tax Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ 2,090	$ 7,305	$ (15,203)
State	1,066	877	1,153
Deferred:
Federal	7,713	3,325	24,686
State	310	307	(6)
Investment Tax Credits	(79)	(79)	(79)
Total Income Tax Expense	$ 11,100	$ 11,735	$ 10,551

Income Taxes (Schedule of Net Deferred Tax Liability) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Utility Plant Related	$ 41,259	$ 69,019
Customer Advances	(3,749)	(3,430)
Employee Benefits	4,903	6,904
Investment Tax Credits (ITC)	675	753
Other	72	(421)
Total Deferred Tax Liability and ITC	$ 43,160	$ 72,825

Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Decreased deferred income tax expense	$ 600
Tax Year 2014 [Member]
Operating Loss Carryforwards [Line Items]
Net reduction in taxes due to the federal government		$ 17,600
Income tax refund receivable		$ 2,300
Deferred Income Taxes [Member]
Operating Loss Carryforwards [Line Items]
Decreased deferred income tax expense	$ 24,200

Commitments and Contingent Liabilities (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) gal	Dec. 31, 2016 USD ($)
Commitment And Contingencies [Line Items]
Period of wastewater agreement	20 years
Guarant liabilty for AWM's performance	$ 100	$ 100
Budgeted construction cost for construction program, 2018	94,000
Budgeted construction cost for construction program, 2019	94,000
Budgeted construction cost for construction program, 2010	79,000
Rental expenses under operating leases	$ 100
Rental commitment under operating lease terms	5 years
NJ Water Supply Authority [Member]
Commitment And Contingencies [Line Items]
Purchase commitment expiration date of contract	Nov. 30, 2023
Water purchase per commitment \| gal	27,000
Regulated Water Authority [Member]
Commitment And Contingencies [Line Items]
Purchase commitment expiration date of contract	Feb. 27, 2021
Water purchase per commitment \| gal	3,000
City of Dover [Member]
Commitment And Contingencies [Line Items]
Water purchase per commitment \| gal	15,000

Commitments and Contingent Liabilities (Schedule of Purchased Water Costs) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Purchased Water
Untreated	$ 2,800	$ 2,600	$ 2,500
Treated	3,300	3,200	3,100
Total Costs	$ 6,100	$ 5,800	$ 5,600

Commitments and Contingent Liabilities (Schedule of Future Minimum Operating Lease) (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Minimum Lease Payments, Sale Leaseback Transactions, Fiscal Year Maturity [Abstract]
2018	$ 700
2019	700
2020	700
2021	700
2022	700
Thereafter	$ 3,800

Short Term Borrowings (Details) - USD ($) $ in Thousands	12 Months Ended
Short Term Borrowings (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Lines Of Credit Facility
Established Lines at Year-End	$ 9,200	$ 60,000
Maximum Amount Outstanding	2,800	13,100
Average Outstanding	18,600	7,400
Notes Payable at Year-End	$ 28,000	$ 12,000
Weighted Average Interest Rate	2.15%	1.54%
Weighted Average Interest Rate at Year-End	2.54%	1.71%

Capitalization (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended		12 Months Ended
	Nov. 30, 2017	Feb. 29, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jul. 31, 2015
Schedule of Capitalization [Line Items]
Shares authorized			40,000,000	40,000,000
Authorized shares under plan			300,000
Issuance of shares under the DRP			$ 1,234	$ 1,453	$ 1,462
Additional Shares Authorized By SEC To Be Issued						700,000
Maximum number of shares authorized for grant			50,000
Preferred Stock, Shares Authorized			126,000	126,000
Preferred Stock, Shares Outstanding			24,000	24,000
Amount drawn			$ 11,523	$ 8,585	7,000
Long-term debt			147,852	142,489
Deobligated principal payments				476	$ 466
Other long term debt			52,500	59,700
Customer advances			$ 21,423	$ 20,846
All Long-term Debt [Member]
Schedule of Capitalization [Line Items]
Weighted average interest rate			3.77%	3.88%
Convertible Preferred Stock $7.00 Series [Member]
Schedule of Capitalization [Line Items]
Shares issued upon conversion			12
Percentage of stock that may be redeemed in a given calander year			10.00%
Convertible Preferred Stock $8.00 Series [Member]
Schedule of Capitalization [Line Items]
Shares issued upon conversion			13.714
Outside Director Stock Compensation Plan [Member]
Schedule of Capitalization [Line Items]
Authorized shares under plan			64,168
Common stock granted and issued under plan			3,976	3,976	4,795
Maximum number of shares authorized for grant			100,000
Dividend Reinvestment and Common Stock Purchase Plan [Member]
Schedule of Capitalization [Line Items]
Issuance of Common Stock			$ 1,200	$ 1,500	$ 1,500
Shares authorized			3,000,000
Dividend Reinvestment & Common Stock Purchase Plan, cumulative shares			2,400
New Jersey Infrastructure Bank [Member]
Schedule of Capitalization [Line Items]
Maximum borrowing capacity, construction loan			$ 9,500
Percentage of principal with stated interest rate			75.00%
Percentage of principal with market interest rate			25.00%
Amount drawn			$ 3,900
Long-term debt			$ 3,800
Interest rate			0.00%
Deobligated principal payments			$ 500
New Jersey Infrastructure Bank [Member] \| Series XX [Member]
Schedule of Capitalization [Line Items]
Maximum borrowing capacity, construction loan	$ 11,300
Percentage of principal with bond interest rate	0.00%
New Jersey Infrastructure Bank [Member] \| Series YY [Member]
Schedule of Capitalization [Line Items]
Maximum borrowing capacity, construction loan	$ 3,900
New Jersey Infrastructure Bank [Member]
Schedule of Capitalization [Line Items]
Amount drawn			$ 14,200
Construction Loan [Member]
Schedule of Capitalization [Line Items]
Interest rate			0.00%
Tidewater [Member]
Schedule of Capitalization [Line Items]
Loan amount		$ 1,200			11,000
Amount drawn		$ 1,100			$ 15,000
Interest rate		2.00%
Maturity date		Feb. 01, 2036			Apr. 30, 2040
Loan amount initially set up as a market-based variable interest rate transaction					$ 4,000
New Jersey Economic Development Authority [Member]
Schedule of Capitalization [Line Items]
Long-term debt			$ 55,400
Delaware State Revolving Fund [Member]
Schedule of Capitalization [Line Items]
Long-term debt			$ 9,100
Maximum [Member]
Schedule of Capitalization [Line Items]
Interest rate					4.47%
Maximum [Member] \| New Jersey Infrastructure Bank [Member] \| Series YY [Member]
Schedule of Capitalization [Line Items]
Percentage of principal with bond interest rate	5.00%
Minimum [Member]
Schedule of Capitalization [Line Items]
Interest rate					4.45%
Minimum [Member] \| New Jersey Infrastructure Bank [Member] \| Series YY [Member]
Schedule of Capitalization [Line Items]
Percentage of principal with bond interest rate	3.00%

Capitalization (Schedule of Maturities of Long-term Debt) (Details) $ in Thousands	Dec. 31, 2017 USD ($)
CAPITALIZATION:
2018	$ 6,900
2019	7,100
2020	6,900
2021	6,900
2022	$ 6,400

Capitalization (Schedule of Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Basic:
Net Income	$ 5,345	$ 7,642	$ 5,381	$ 4,441	$ 3,220	$ 8,813	$ 5,919	$ 4,790	$ 22,809	$ 22,742	$ 20,028
Preferred Dividend									(144)	(144)	(144)
Earnings Applicable to Common Stock									$ 22,665	$ 22,598	$ 19,884
Weighted-average number of basic shares outstanding, shares									16,330,000	16,270,000	16,175,000
Basic EPS	$ 0.32	$ 0.47	$ 0.33	$ 0.27	$ 0.20	$ 0.54	$ 0.36	$ 0.29	$ 1.39	$ 1.39	$ 1.23
Diluted:
$7.00 Series Preferred Dividend									$ 67	$ 67	$ 67
$8.00 Series Preferred Dividend									24	24	24
Adjusted Earnings Applicable to Common Stock									$ 22,756	$ 22,689	$ 19,975
Incremental common shares attributable to $7.00 series preferred shares, shares									115,000	115,000	115,000
Incremental common shares attributable to $8.00 series preferred shares, shares									41,000	41,000	41,000
Weighted-average diluted shares outstanding, shares									16,486,000	16,426,000	16,331,000
Diluted EPS	$ 0.32	$ 0.46	$ 0.33	$ 0.27	$ 0.19	$ 0.54	$ 0.36	$ 0.29	$ 1.38	$ 1.38	$ 1.22

Capitalization (Schedule of Carrying Amount and Fair Value of Bonds) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Carrying amount [Member]
Bonds	$ 95,322	$ 82,786
Fair value [Member]
Bonds	$ 98,036	$ 88,431

Employee Benefit Plans (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated benefit obligation		$ 75,700	$ 66,800
Increase (decrease) in annual rate per capita cost of covered healthcare benefits, next year		9.00%
Increase (decrease) in annual rate per capita cost of covered healthcare benefits, 2019-2021		1.00%
Increase (decrease) in annual rate per capita cost of covered healthcare benefits, 2022-2023		0.50%
Annual rate of increase in the per capita cost of covered healthcare benefits		5.00%
Number of hours required to participate in contribution plan		1,000
Percent of participants contributions matched by company, below one percent of participants compensation		100.00%
Percent of participants contributions matched by company, above one percent of participants compensation		50.00%
Threshold percentage of participants compensation at which matching decreases		1.00%
Matching contributions, percent		6.00%
Matching contributions		$ 600	600	$ 600
Discretionary contributions, percent		5.00%
Discretionary contributions		$ 500	400	$ 400
Escrow account maintained for 2008 restricted stock plan		100
Maximum number of shares authorized for grant		300,000
Number of shares authorized for grant, unissued		50,000
Fair value of vested restricted shares		$ 800	$ 900
Middlesex [Member] \| Equity Securities [Member]
Allocation of plan assets		1.10%	1.40%
Common stock in plan, value		$ 800	$ 800
Pension Benefit Plan [Member]
Allocation of plan assets		100.00%	100.00%
Benfit plan, Cash contributions		$ 3,600
Pension Benefit Plan [Member] \| Equity Securities [Member]
Allocation of plan assets		62.80%	59.70%
Pension Benefit Plan [Member] \| Scenario, Forecast [Member]
Benfit plan, Cash contributions	$ 3,300
Other Benefits Plan [Member]
Allocation of plan assets		100.00%	100.00%
Benfit plan, Cash contributions		$ 1,600
Other Benefits Plan [Member] \| Equity Securities [Member]
Allocation of plan assets		57.70%	54.10%
Other Benefits Plan [Member] \| Scenario, Forecast [Member]
Benfit plan, Cash contributions	$ 1,600

Employee Benefit Plans (Schedule of Change in Projected Benefit Obligation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Benefit Plan [Member]
Change in Projected Benefit Obligation:
Beginning Balance	$ 78,601	$ 72,542
Service Cost	2,399	2,308	$ 2,558
Interest Cost	3,143	3,046	2,894
Actuarial Loss	6,203	2,810
Benefits Paid	(2,333)	(2,105)
Ending Balance	88,013	78,601	72,542
Other Benefits Plan [Member]
Change in Projected Benefit Obligation:
Beginning Balance	48,888	46,249
Service Cost	1,089	1,099	1,373
Interest Cost	1,964	1,952	1,921
Actuarial Loss	3,052	141
Benefits Paid	(648)	(553)
Ending Balance	$ 54,345	$ 48,888	$ 46,249

Employee Benefit Plans (Schedule of Change in Fair Value of Plan Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Pension Benefit Plan [Member]
Change in Fair Value of Plan Assets:
Beginning Balance	$ 59,370	$ 52,931
Actual Return on Plan Assets	8,543	4,909
Employer Contributions	3,635	3,635
Benefits Paid	(2,333)	(2,105)
Ending Balance	69,215	59,370
Funded Status	(18,798)	(19,231)
Other Benefits Plan [Member]
Change in Fair Value of Plan Assets:
Beginning Balance	31,607	29,018
Actual Return on Plan Assets	3,521	1,591
Employer Contributions	1,603	1,551
Benefits Paid	(648)	(553)
Ending Balance	36,083	31,607
Funded Status	$ (18,262)	$ (17,281)

Employee Benefit Plans (Schedule of Employee Benefit Plans Recognized in Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Noncurrent Liability	$ 36,686	$ 36,139
Pension Benefit Plan [Member]
Current Liability	374	373
Noncurrent Liability	18,424	18,858
Net Liability Recognized	18,798	19,231
Other Benefits Plan [Member]
Current Liability
Noncurrent Liability	18,262	17,281
Net Liability Recognized	$ 18,262	$ 17,281

Employee Benefit Plans (Schedule of Periodic Costs For Employee Retirement Benefit Plans) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Benefit Plan [Member]
Periodic costs for employee retirement benefit plans
Service Cost	$ 2,399	$ 2,308	$ 2,558
Interest Cost	3,143	3,046	2,894
Expected Return on Plan Assets	(4,489)	(4,014)	(3,919)
Amortization of Net Actuarial Loss	1,566	1,426	1,645
Amortization of Prior Service Credit
Net Periodic Benefit Cost	2,619	2,766	3,178
Other Benefits Plan [Member]
Periodic costs for employee retirement benefit plans
Service Cost	1,089	1,099	1,373
Interest Cost	1,964	1,952	1,921
Expected Return on Plan Assets	(2,406)	(2,213)	(2,107)
Amortization of Net Actuarial Loss	1,781	1,773	2,261
Amortization of Prior Service Credit	(1,728)	(1,728)	(1,728)
Net Periodic Benefit Cost	$ 700	$ 883	$ 1,720

Employee Benefit Plans (Schedule of Amounts Expected to be Amortized from Regulatory Assets to Net Periodic Benefit Cost) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Pension Benefit Plan [Member]
Actuarial Loss	$ 1,658
Prior Service Credit
Other Benefits Plan [Member]
Actuarial Loss	1,787
Prior Service Credit	$ (1,607)

Employee Benefit Plans (Schedule of Discount and Compensation Rates) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Benefit Plan [Member]
Weighted Average Assumptions:
Expected Return on Plan Assets	7.50%	7.50%	7.50%
Discount Rate for:
Benefit Obligation	3.53%	4.06%	4.26%
Benefit Cost	4.06%	4.26%	3.91%
Compensation Increase for:
Benefit Obligation	3.00%	3.00%	3.00%
Benefit Cost	3.00%	3.00%	3.00%
Other Benefits Plan [Member]
Weighted Average Assumptions:
Expected Return on Plan Assets	7.50%	7.50%	7.50%
Discount Rate for:
Benefit Obligation	3.53%	4.06%	4.26%
Benefit Cost	4.06%	4.26%	3.91%
Compensation Increase for:
Benefit Obligation	3.00%	3.00%	3.00%
Benefit Cost	3.00%	3.00%	3.00%

Employee Benefit Plans (Schedule of Effect of One-percentage Point Change in Assumed Health Care Cost Trend Rates) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Pension Benefit Plan [Member]
Effect on Current Year's Service and Interest Cost - Increase	$ 649
Effect on Projected Benefit Obligation - Increase	9,412
Other Benefits Plan [Member]
Effect on Current Year's Service and Interest Cost - Decrease	(499)
Effect on Projected Benefit Obligation - Decrease	$ (7,403)

Employee Benefit Plans (Schedule of Expected Benefit Payments) (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Other Benefits Plan [Member]
2018	$ 2,639
2019	2,653
2020	2,875
2021	2,971
2022	3,360
2023-2027	23,789
Totals	38,287
Pension Benefit Plan [Member]
2018	1,174
2019	1,414
2020	1,614
2021	1,816
2022	2,027
2023-2027	11,674
Totals	$ 19,719

Employee Benefit Plans (Schedule of Allocation of Plan Assets) (Details)	Dec. 31, 2017	Dec. 31, 2016
Pension Benefit Plan [Member]
Allocation of plan assets	100.00%	100.00%
Pension Benefit Plan [Member] \| Commodities [Member]
Allocation of plan assets	2.60%	2.70%
Target plan allocations	5.00%
Pension Benefit Plan [Member] \| Cash [Member]
Allocation of plan assets	1.00%	1.00%
Target plan allocations	2.00%
Pension Benefit Plan [Member] \| Debt Securities [Member]
Allocation of plan assets	33.60%	36.60%
Target plan allocations	38.00%
Pension Benefit Plan [Member] \| Equity Securities [Member]
Allocation of plan assets	62.80%	59.70%
Target plan allocations	55.00%
Other Benefits Plan [Member]
Allocation of plan assets	100.00%	100.00%
Other Benefits Plan [Member] \| Commodities [Member]
Allocation of plan assets	0.00%	0.00%
Target plan allocations	5.00%
Other Benefits Plan [Member] \| Cash [Member]
Allocation of plan assets	9.40%	2.60%
Target plan allocations	2.00%
Other Benefits Plan [Member] \| Debt Securities [Member]
Allocation of plan assets	32.90%	43.30%
Target plan allocations	50.00%
Other Benefits Plan [Member] \| Equity Securities [Member]
Allocation of plan assets	57.70%	54.10%
Target plan allocations	43.00%

Employee Benefit Plans (Schedule of Fair Value of Pension Plan Assets) (Details) - Pension Benefit Plan [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair value of plan assets	$ 69,215	$ 59,370	$ 52,931
Fair Value, Level 1 [Member]
Fair value of plan assets	69,215	59,370
Fair Value, Level 2 [Member]
Fair value of plan assets
Fair Value, Level 3 [Member]
Fair value of plan assets
Equity Securities [Member]
Fair value of plan assets	10,930	9,283
Equity Securities [Member] \| Fair Value, Level 2 [Member]
Fair value of plan assets
Equity Securities [Member] \| Fair Value, Level 3 [Member]
Fair value of plan assets
Mutual Funds [Member]
Fair value of plan assets	57,608	49,439
Mutual Funds [Member] \| Fair Value, Level 1 [Member]
Fair value of plan assets	57,608	49,439
Mutual Funds [Member] \| Fair Value, Level 2 [Member]
Fair value of plan assets
Mutual Funds [Member] \| Fair Value, Level 3 [Member]
Fair value of plan assets
Money Market Funds [Member]
Fair value of plan assets	677	648
Money Market Funds [Member] \| Fair Value, Level 1 [Member]
Fair value of plan assets	677	648
Money Market Funds [Member] \| Fair Value, Level 2 [Member]
Fair value of plan assets
Money Market Funds [Member] \| Fair Value, Level 3 [Member]
Fair value of plan assets
Equity Securities [Member] \| Fair Value, Level 1 [Member]
Fair value of plan assets	10,930	$ 9,283
Equity Securities [Member] \| Fair Value, Level 2 [Member]
Fair value of plan assets

Employee Benefit Plans (Schedule of Fair Value of Other Benefits Plan Assets) (Details) - Other Benefits Plan [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair value of plan assets	$ 36,083	$ 31,607	$ 29,018
Fair Value, Level 1 [Member]
Fair value of plan assets	24,322	18,030
Fair Value, Level 2 [Member]
Fair value of plan assets	11,761	13,577
Fair Value, Level 3 [Member]
Fair value of plan assets
Debt Securities [Member]
Fair value of plan assets		13,577
Mutual Funds [Member]
Fair value of plan assets	20,819	17,096
Mutual Funds [Member] \| Fair Value, Level 1 [Member]
Fair value of plan assets	20,819	17,096
Mutual Funds [Member] \| Fair Value, Level 2 [Member]
Fair value of plan assets
Mutual Funds [Member] \| Fair Value, Level 3 [Member]
Fair value of plan assets
Money Market Funds [Member]
Fair value of plan assets	3,388	826
Money Market Funds [Member] \| Fair Value, Level 1 [Member]
Fair value of plan assets	3,388	826
Money Market Funds [Member] \| Fair Value, Level 2 [Member]
Fair value of plan assets
Money Market Funds [Member] \| Fair Value, Level 3 [Member]
Fair value of plan assets
Preferred Equity Securities [Member]
Fair value of plan assets	115	108
Preferred Equity Securities [Member] \| Fair Value, Level 1 [Member]
Fair value of plan assets	115	108
Preferred Equity Securities [Member] \| Fair Value, Level 2 [Member]
Fair value of plan assets
Preferred Equity Securities [Member] \| Fair Value, Level 3 [Member]
Fair value of plan assets
Debt Securities [Member]
Fair value of plan assets	11,761
Debt Securities [Member] \| Fair Value, Level 1 [Member]
Fair value of plan assets
Debt Securities [Member] \| Fair Value, Level 2 [Member]
Fair value of plan assets	11,761	13,577
Debt Securities [Member] \| Fair Value, Level 3 [Member]
Fair value of plan assets

Employee Benefit Plans (Schedule of Restricted Stock Plan) (Details) - 2008 Restricted Stock Plan [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Shares
Balance	147,000	148,000	127,000
Granted	22,000	24,000	33,000
Vested	(20,000)	(25,000)	(12,000)
Forfeited	(2,000)
Amortization of Compensation Expense
Balance	147,000	147,000	148,000
Unearned compensation
Balance	$ 1,764	$ 1,696	$ 1,483
Granted	799	750	741
Vested
Forfeited	(54)
Amortization of Compensation Expense	(724)	(682)	(528)
Balance	$ 1,785	$ 1,764	$ 1,696
Weighted Average Grant Price
Granted	$ 36.95	$ 30.85	$ 22.65

Business Segment Data (Details) $ in Thousands	3 Months Ended								12 Months Ended
Business Segment Data (Details) $ in Thousands	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments									2	2
Revenues	$ 31,456	$ 36,174	$ 33,014	$ 30,131	$ 31,808	$ 37,754	$ 32,725	$ 30,579	$ 130,775	$ 132,906	$ 126,025
Operating Income	8,471	12,806	9,563	7,780	7,846	14,156	10,328	8,302	38,620	40,632	35,840
Depreciation									13,922	12,796	12,051
Other Income (Expense), Net									795	(862)	293
Interest Expense									5,506	5,293	5,554
Income Taxes									11,100	11,735	10,551
Net Income	5,345	$ 7,642	$ 5,381	$ 4,441	3,220	$ 8,813	$ 5,919	$ 4,790	22,809	22,742	20,028
Capital Expenditures									50,301	47,375	25,773
Assets	661,140				620,161				661,140	620,161
Inter-segment Elimination [Member]
Segment Reporting Information [Line Items]
Revenues									(591)	(499)	(460)
Other Income (Expense), Net									(467)	(333)	(346)
Interest Expense									(467)	(89)	(89)
Assets	(7,769)				(5,999)				(7,769)	(5,999)
Regulated [Member]
Segment Reporting Information [Line Items]
Revenues									115,454	118,017	111,247
Operating Income									35,952	38,201	33,603
Depreciation									13,732	12,606	11,874
Other Income (Expense), Net									1,198	779	619
Interest Expense									5,855	5,293	5,554
Income Taxes									9,848	11,091	9,522
Net Income									21,447	22,353	18,889
Capital Expenditures									50,078	47,189	25,706
Assets	661,816				619,915				661,816	619,915
Non - Regulated [Member]
Segment Reporting Information [Line Items]
Revenues									15,912	15,388	15,238
Operating Income									2,668	2,431	2,237
Depreciation									190	190	177
Other Income (Expense), Net									64	(1,308)	20
Interest Expense									118	89	89
Income Taxes									1,252	644	1,029
Net Income									1,362	389	1,139
Capital Expenditures									223	186	$ 67
Assets	$ 7,093				$ 6,245				$ 7,093	$ 6,245

Quarterly Operating Results - Unaudited (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Operating Revenues	$ 31,456	$ 36,174	$ 33,014	$ 30,131	$ 31,808	$ 37,754	$ 32,725	$ 30,579	$ 130,775	$ 132,906	$ 126,025
Operating Income	8,471	12,806	9,563	7,780	7,846	14,156	10,328	8,302	38,620	40,632	35,840
Net Income	$ 5,345	$ 7,642	$ 5,381	$ 4,441	$ 3,220	$ 8,813	$ 5,919	$ 4,790	$ 22,809	$ 22,742	$ 20,028
Basic Earnings per Share	$ 0.32	$ 0.47	$ 0.33	$ 0.27	$ 0.20	$ 0.54	$ 0.36	$ 0.29	$ 1.39	$ 1.39	$ 1.23
Diluted Earnings per Share	$ 0.32	$ 0.46	$ 0.33	$ 0.27	$ 0.19	$ 0.54	$ 0.36	$ 0.29	$ 1.38	$ 1.38	$ 1.22