Commitments and Contingent Liabilities (Narrative) (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($) gal	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Purchase Commitment, Excluding Long-term Commitment [Line Items]
Guaranty liabilty for AWM's performance | $	$ 100		$ 100
Budgeted construction cost for construction program, 2018 | $	78,000
Rental expenses under operating leases | $	$ 100	$ 100
NJ Water Supply Authority [Member]
Purchase Commitment, Excluding Long-term Commitment [Line Items]
Purchase commitment expiration date of contract	Nov. 30, 2023
Water purchase per commitment | gal	27,000,000
Regulated Water Authority [Member]
Purchase Commitment, Excluding Long-term Commitment [Line Items]
Purchase commitment expiration date of contract	Feb. 27, 2021
Water purchase per commitment | gal	3,000,000
City of Dover [Member]
Purchase Commitment, Excluding Long-term Commitment [Line Items]
Water purchase per commitment | gal	15,000,000