Commitments and Contingent Liabilities (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) gal	Dec. 31, 2015 USD ($)
Commitment And Contingencies [Line Items]
Period of wastewater agreement	20 years
Guarant liabilty for AWM's performance	$ 100	$ 200
Budgeted construction cost for construction program, 2017	60,200
Budgeted construction cost for construction program, 2018	88,900
Budgeted construction cost for construction program, 2019	$ 73,800
NJ Water Supply Authority [Member]
Commitment And Contingencies [Line Items]
Purchase commitment expiration date of contract	Nov. 30, 2023
Water purchase per commitment | gal	27,000,000
Regulated Water Authority [Member]
Commitment And Contingencies [Line Items]
Purchase commitment expiration date of contract	Feb. 27, 2021
Water purchase per commitment | gal	3,000,000
City of Dover [Member]
Commitment And Contingencies [Line Items]
Water purchase per commitment | gal	15,000,000