Summary of Significant Accounting Policies (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Summary of Significant Accounting Policies [Line Items]
Markup for return or profit for cost-recovery expenses			$ 0
Maturity period of commercial paper			90 days
Minimum collection period after net receivable balances were recognized in which the Company defers net WRAM and MCBA operating revenues and associated costs			24 months
Maximum collection period in which deferred net WRAM and MCBA revenues and associated costs will be recognized			24 months
Unearned revenue liability	$ 700,000		$ 700,000		$ 800,000
Allowance for equity funds used during construction	1,105,000	$ 0	2,763,000	$ 0
Allowance for borrowed funds used during construction	707,000	774,000	1,765,000	2,341,000
Allowance for Equity and Borrowed Funds Used During Construction	1,812,000	774,000	4,528,000	2,341,000
Allowance for equity funds used during construction, Change	1,105,000		2,763,000
Allowance for borrowed funds used during construction, Change	(67,000)		(576,000)
Allowance for Equity and Borrowed Funds Used During Construction, Change	1,038,000		2,187,000
Carrying value of cash and cash equivalents	28,341,000	$ 21,351,000	28,341,000	21,351,000	25,492,000	$ 8,837,000
Income tax benefits in excess compensation costs for share-based compensation			500,000
Other changes in noncurrent assets and liabilities			41,837,000	34,386,000
Net cash provided by operating activities				123,829,000
Repurchase of common stock			(1,359,000)	(637,000)
Net cash provided by financing activities				57,991,000
As Reported on Form 10-Q
Summary of Significant Accounting Policies [Line Items]
Other changes in noncurrent assets and liabilities				33,749,000
Net cash provided by operating activities				123,192,000
Repurchase of common stock				0
Net cash provided by financing activities				58,628,000
Increase (Decrease) from Retrospective Adoption | Accounting Standards Update 2016-09
Summary of Significant Accounting Policies [Line Items]
Other changes in noncurrent assets and liabilities				637,000
Net cash provided by operating activities				637,000
Repurchase of common stock				(637,000)
Net cash provided by financing activities				$ (637,000)
Taxes, prepaid expenses and other assets
Summary of Significant Accounting Policies [Line Items]
Carrying value of restricted cash	$ 1,100,000		$ 1,100,000		$ 400,000
Minimum
Summary of Significant Accounting Policies [Line Items]
Expected collection period for undercollected net WRAM and MCBA receivables			12 months
Maximum
Summary of Significant Accounting Policies [Line Items]
Expected collection period for undercollected net WRAM and MCBA receivables			18 months