Summary of Significant Accounting Policies (Revenue, Balancing and Memorandum Accounts) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue from External Customer [Line Items]
Regulated operating revenue, water surcharge	$ 5,235	$ 3,807	$ 4,605
San Jose Water Company [Member]
Revenue from External Customer [Line Items]
Nonregulated operating revenue	$ 7,419	$ 6,451	$ 6,145