Capitalization (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Nov. 30, 2017	Mar. 31, 2018	Mar. 31, 2017	Apr. 30, 2018	Dec. 31, 2017	Aug. 31, 2017
Schedule of Capitalization [Line Items]
Issuance of shares under the DRP, shares		7,665	7,845
Issuance of shares under the DRP		$ 300	$ 300
Other long term debt		54,000			$ 52,500
Customer advances		21,024			$ 21,423
Amount drawn		2,293	$ 2,738
New Jersey Infrastructure Bank [Member]
Schedule of Capitalization [Line Items]
Amount drawn		14,800
Middlesex [Member]
Schedule of Capitalization [Line Items]
Amount drawn		6,200
Series XX [Member]
Schedule of Capitalization [Line Items]
Proceeds from issuance of first mortgage bond	$ 11,300
Interest rate	0.00%
Due date of debt	Aug. 01, 2047
Series YY [Member]
Schedule of Capitalization [Line Items]
Proceeds from issuance of first mortgage bond	$ 3,900
Due date of debt	Aug. 01, 2047
Series YY [Member] | Minimum [Member]
Schedule of Capitalization [Line Items]
Interest rate	3.00%
Series YY [Member] | Maximum [Member]
Schedule of Capitalization [Line Items]
Interest rate	5.00%
New Jersey NJIB Program [Member]
Schedule of Capitalization [Line Items]
Maximum borrowing amount		14,000
Maximum borrowing capacity, construction loan						$ 9,500
New Jersey NJIB Program [Member] | Subsequent Event [Member]
Schedule of Capitalization [Line Items]
Maximum borrowing amount				$ 57,000
Maximum borrowing capacity, construction loan				$ 55,000
Delaware State Revolving Fund [Member]
Schedule of Capitalization [Line Items]
Maximum borrowing amount		$ 900