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Summary of Significant Accounting Policies (Investment in California Water Service Group) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Public Utilities, General Disclosures [Line Items]
Available for Sale Marketable Security, Shares Held	0
Available for Sale Marketable Security, Shares Sold	100,000		159,151
Proceeds from Sale of Debt Securities, Available-for-sale	$ 4,510
Proceeds from sale of California Water Service Group stock	4,112	$ 0	$ 4,509
Fees Incurred on Sale of Available for Sale Securities	9		20
Gain on sale of California Water Service Group stock	104	0	3,197
Available for Sales Securities, Tax on Realized Gain	29		1,303
Debt and Equity Securities, Gain (Loss)	75		1,894
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	0	0	$ 1,742
Quoted Prices in Active Markets for Identical Assets (Level 1)
Public Utilities, General Disclosures [Line Items]
Available-for-sale Securities	$ 0	$ 4,535

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