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Capitalization (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended			3 Months Ended		9 Months Ended
	Oct. 31, 2019	Aug. 31, 2019	May 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	May 31, 2019	Apr. 30, 2019	Feb. 28, 2019	Dec. 31, 2018	Aug. 31, 2018	Mar. 31, 2018
Schedule of Capitalization [Line Items]
Issuance of shares under the DRP, shares						221,558	21,001
Issuance of shares under the DRP				$ 5,368	$ 266	$ 12,449	$ 864
Common stock granted and issued under plan		200,000
Percentage of offering shares on discount to participants		5.00%
Convertible Preferred Stock Converted				41,142		41,142
Due date of debt						Sep. 30, 2019
Other long term debt				$ 80,500		$ 80,500					$ 61,500
Customer advances				$ 22,682		22,682					$ 22,572
Amount drawn						82,446	9,265
Deobligated principal payments						$ 130
Subsequent Event [Member]
Schedule of Capitalization [Line Items]
Number of shares purchased	232,643
Average price per share	$ 55.79
Series Cumulative Preferred Stock [Member]
Schedule of Capitalization [Line Items]
Number of shares purchased						3,000
Number of shares purchased value						$ 300,000
No par value				$ 8.00		$ 8.00
New Jersey NJIB Program [Member]
Schedule of Capitalization [Line Items]
Maximum borrowing capacity, construction loan					$ 8,700		$ 8,700
Delaware State Revolving Fund [Member]
Schedule of Capitalization [Line Items]
Maximum borrowing amount													$ 900
Maximum borrowing capacity, construction loan									$ 1,700
Series 2018A [Member]
Schedule of Capitalization [Line Items]
Proceeds from issuance of first mortgage bond			$ 7,100
Interest rate			0.00%
Due date of debt			Aug. 01, 2047
Series 2018B [Member]
Schedule of Capitalization [Line Items]
Proceeds from issuance of first mortgage bond			$ 2,400
Due date of debt			Aug. 01, 2047
Series 2019A [Member]
Schedule of Capitalization [Line Items]
Maximum borrowing capacity, construction loan		$ 32,500
Interest rate		4.00%
Series 2019B [Member]
Schedule of Capitalization [Line Items]
Maximum borrowing capacity, construction loan		$ 21,200
Interest rate		5.00%
New Jersey Infrastructure Bank [Member]
Schedule of Capitalization [Line Items]
Maximum borrowing capacity, construction loan			$ 9,500							$ 140,000		$ 43,500
Interest rate				0.00%		0.00%
Percentage of principal with stated interest rate						75.00%
Percentage of principal with market interest rate						25.00%
Deobligated principal payments						$ 100
Amount of drawn expected remaining						8,000
Middlesex [Member]
Schedule of Capitalization [Line Items]
Maximum borrowing capacity, construction loan				$ 30,200		30,200
First Mortgage Bonds [Member]
Schedule of Capitalization [Line Items]
Maximum borrowing capacity, construction loan		$ 53,700		$ 60,800		60,800
Amount drawn						7,600
Proceeds from issuance premium		$ 7,100
Amount of drawn expected remaining						$ 53,200
Maximum [Member]
Schedule of Capitalization [Line Items]
Percentage of offering shares on discount to participants						5.00%
Maximum [Member] \| Series 2018B [Member]
Schedule of Capitalization [Line Items]
Interest rate			5.00%
Minimum [Member] \| Series 2018B [Member]
Schedule of Capitalization [Line Items]
Interest rate			3.00%
New Jersey Board Of Public Utilities [Member]
Schedule of Capitalization [Line Items]
Authorized shares under plan								1,500,000