Commitments and Contingent Liabilities (Narrative) (Details) $ in Thousands, gal in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) gal	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Commitment And Contingencies [Line Items]
Guarant liabilty for AWM's performance	$ 1,400	$ 1,500
Budgeted construction cost for construction program, 2020	124,000
Budgeted construction cost for construction program, 2021	112,000
Budgeted construction cost for construction program, 2022	59,000
Rental expenses under operating leases	700	$ 500	$ 1
Estimated obligation expend	$ 63,000
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, 2021
Water purchase per commitment | gal	3.0
City of Dover [Member]
Commitment And Contingencies [Line Items]
Water purchase per commitment | gal	15.0