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Rate and Regulatory Matters (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended			12 Months Ended
	Feb. 28, 2019	Mar. 31, 2018	Oct. 17, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Regulatory Liabilities [Line Items]
Regulatory Liability - Cost of Utility Plant Removal				$ 79,112	$ 43,745
Regulatory liabilities				31,700	31,600
Deferred income tax benefits				(8,724)	$ 7,944	$ 3,553
Subsequent Event [Member]
Regulatory Liabilities [Line Items]
Corporate tax rate	3.35%
Maximum [Member]
Regulatory Liabilities [Line Items]
Base rate amount				$ 4,900
Corporate tax rate				35.00%
Minimum [Member]
Regulatory Liabilities [Line Items]
Base rate amount				$ 10,400
Corporate tax rate				21.00%
Middlesex [Member]
Regulatory Liabilities [Line Items]
Base rate amount			$ 15,300
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
Twin Lakes [Member]
Regulatory Liabilities [Line Items]
Approved increase in annual operating revenues						$ 100
New Jersey Board Of Public Utilities [Member] | Middlesex [Member]
Regulatory Liabilities [Line Items]
Approved increase in annual operating revenues		$ 5,500
Additional annual costs				$ 100
Base rate amount		$ 245,500
Return on equity		9.60%
Regulatory liabilities				34,600
Deferred income tax benefits		$ 28,700
Amortization period		4 years
Delaware Public Service Commission [Member] | Tidewater [Member]
Regulatory Liabilities [Line Items]
Approved increase in annual operating revenues				200
Delaware Public Service Commission [Member] | Southern Shores [Member]
Regulatory Liabilities [Line Items]
Originally filed increase in annual operating revenue				$ 100

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