Rate and Regulatory Matters (Narrative) (Details) $ in Thousands			1 Months Ended				12 Months Ended
	Nov. 04, 2019 USD ($)	Mar. 01, 2019	Nov. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Nov. 30, 2019 USD ($) Customer	Mar. 31, 2018 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Regulatory Liabilities [Line Items]
Corporate tax rate		3.35%
Regulatory liabilities							$ 31,000	$ 31,500
Deferred income tax benefits							$ (13,490)	(11,719)	$ (8,724)
Maximum [Member]
Regulatory Liabilities [Line Items]
Corporate tax rate							35.00%
Minimum [Member]
Regulatory Liabilities [Line Items]
Corporate tax rate							21.00%
Delaware Public Service Commission [Member]
Regulatory Liabilities [Line Items]
Percentage of consumer price index							3.00%
Maturity date							Dec. 31, 2029
Delaware Public Service Commission [Member] | Tidewater [Member]
Regulatory Liabilities [Line Items]
Approved increase in annual operating revenues							$ 600
Number of customers | Customer					1,000
Purchase of the wastewater utility assets					$ 18
New Jersey Board Of Public Utilities [Member] | Middlesex [Member]
Regulatory Liabilities [Line Items]
Approved increase in annual operating revenues			$ 1,100			$ 5,500
Additional annual costs				$ 600
Base rate amount						$ 245,500
Return on equity						9.60%
Regulatory liabilities							14,900	$ 24,200
Deferred income tax benefits						$ 28,700
Amortization period						4 years
New Jersey Board Of Public Utilities [Member] | Pinelands Wastewater [Member]
Regulatory Liabilities [Line Items]
Approved increase in annual operating revenues	$ 500
Pennsylvania Public Utilities Commissio [Member] | Twin Lakes [Member]
Regulatory Liabilities [Line Items]
Base rate amount							1,500
Revenues							$ 200