Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Regulatory Assets and Liabilities
Regulatory assets	$ 367,476	$ 355,930
Regulatory liabilities	37,945	38,735
Short-term portion of the regulatory assets	30,661	30,332
Short-term portion of the regulatory liabilities	8,197	4,759
Tax benefits to ratepayers
Regulatory Assets and Liabilities
Regulatory liabilities	33,271	33,231
Conservation program
Regulatory Assets and Liabilities
Regulatory liabilities	1,034	584
Pension balancing account
Regulatory Assets and Liabilities
Regulatory liabilities	82	695
Net WRAM and MCBA long-term payable
Regulatory Assets and Liabilities
Regulatory liabilities	566	611
Other regulatory liabilities
Regulatory Assets and Liabilities
Regulatory liabilities	2,992	3,614
Pension and retiree group health
Regulatory Assets and Liabilities
Regulatory assets	188,715	188,880
Tax benefits to ratepayers
Regulatory Assets and Liabilities
Regulatory assets	92,676	92,099
Other accrued benefits
Regulatory Assets and Liabilities
Regulatory assets	26,456	27,503
Net WRAM and MCBA long-term accounts receivable
Regulatory Assets and Liabilities
Regulatory assets	27,300	16,148
Asset retirement obligations, net
Regulatory Assets and Liabilities
Regulatory assets	16,148	15,812
Interim rates long-term accounts receivable
Regulatory Assets and Liabilities
Regulatory assets	4,597	4,605
Tank coating
Regulatory Assets and Liabilities
Regulatory assets	8,922	8,452
Health care balancing account
Regulatory Assets and Liabilities
Regulatory assets	96	1,000
Pension cost balancing account
Regulatory Assets and Liabilities
Regulatory assets	510	0
Other regulatory assets
Regulatory Assets and Liabilities
Regulatory assets	$ 2,056	$ 1,431