Commitments and Contingent Liabilities (Narrative) (Details) $ in Thousands, gal in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) gal	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Commitment And Contingencies [Line Items]
Guarant liabilty for AWM's performance	$ 0	$ 1,400
Budgeted construction cost for construction program, 2021	134,000
Budgeted construction cost for construction program, 2022	97,000
Budgeted construction cost for construction program, 2023	83,000
Rental expenses under operating leases	800	$ 700	$ 500
Estimated obligation expend	$ 19,000
Estimated incremental borrowing rate	4.03%
Lease maturity date	2030
NJ Water Supply Authority [Member]
Commitment And Contingencies [Line Items]
Purchase commitment expiration date of contract	Nov. 30, 2023
Water purchase per commitment | gal	27.0
Regulated Water Authority [Member]
Commitment And Contingencies [Line Items]
Purchase commitment expiration date of contract	Feb. 27, 2026
Water purchase per commitment | gal	3.0
City of Dover [Member]
Commitment And Contingencies [Line Items]
Water purchase per commitment | gal	15.0