Commitments and Contingent Liabilities (Schedule of Purchased Water Costs) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Purchased Water
Untreated	$ 2,600	$ 2,500	$ 2,400
Treated	3,200	3,100	3,100
Total Costs	$ 5,800	$ 5,600	$ 5,500