Summary of Significant Accounting Policies (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Summary of Significant Accounting Policies [Line Items]
Markup for return or profit for cost-recovery expenses	$ 0
Maturity period of commercial paper	90 days
Expected collection period for undercollected net WRAM and MCBA receivables	18 months
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	$ 900,000	$ 1,300,000
Carrying value of cash and cash equivalents	21,351,000	8,837,000	$ 50,825,000	$ 19,587,000
Long-term debt unamortized debt issuance costs	4,600,000	4,800,000
Other assets	50,953,000	47,399,000
Long-term debt, less current maturities	555,536,000	508,002,000
Current maturities of long-term debt	6,130,000	6,043,000
As Reported on Form 10-K
Summary of Significant Accounting Policies [Line Items]
Other assets		52,241,000
Long-term debt, less current maturities		512,287,000
Current maturities of long-term debt		6,600,000
Decrease from Retrospective Adoption
Summary of Significant Accounting Policies [Line Items]
Other assets		(4,842,000)
Long-term debt, less current maturities		(4,285,000)
Current maturities of long-term debt		(557,000)
Taxes, prepaid expenses and other assets [Member]
Summary of Significant Accounting Policies [Line Items]
Carrying value of restricted cash	$ 1,200,000	$ 500,000
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		20 months
Accounting Standards Update 2012-03 [Member]
Summary of Significant Accounting Policies [Line Items]
Other assets		$ 47,399,000
Long-term debt, less current maturities		508,002,000
Current maturities of long-term debt		$ 6,043,000