Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Regulatory Assets and Liabilities
Regulatory assets	$ 405,041	$ 401,147
Regulatory liabilities	187,066	179,706
Short-term portion of the regulatory assets	34,119	36,783
Short-term portion of the regulatory liabilities	56,206	59,303
Property-related temporary differences (tax benefits flowed through to customers)
Regulatory Assets and Liabilities
Regulatory liabilities	168,366	168,343
Health care balancing account
Regulatory Assets and Liabilities
Regulatory liabilities	9,282	7,749
Conservation program
Regulatory Assets and Liabilities
Regulatory liabilities	3,797	2,273
Pension balancing account
Regulatory Assets and Liabilities
Regulatory liabilities	154	364
Net WRAM and MCBA long-term payable
Regulatory Assets and Liabilities
Regulatory liabilities	2,035	513
Tax accounting memorandum account
Regulatory Assets and Liabilities
Regulatory liabilities	1,982	0
Cost of capital memorandum account
Regulatory Assets and Liabilities
Regulatory liabilities	1,151	0
Other regulatory liabilities
Regulatory Assets and Liabilities
Regulatory liabilities	299	464
Pension and retiree group health
Regulatory Assets and Liabilities
Regulatory assets	214,084	214,249
Property-related temporary differences (tax benefits flowed through to customers)
Regulatory Assets and Liabilities
Regulatory assets	87,700	87,323
Other accrued benefits
Regulatory Assets and Liabilities
Regulatory assets	29,073	28,251
Net WRAM and MCBA long-term accounts receivable
Regulatory Assets and Liabilities
Regulatory assets	35,278	34,879
Asset retirement obligations, net
Regulatory Assets and Liabilities
Regulatory assets	17,473	17,126
Interim rates long-term accounts receivable
Regulatory Assets and Liabilities
Regulatory assets	4,568	4,568
Tank coating
Regulatory Assets and Liabilities
Regulatory assets	11,052	10,998
Health care balancing account
Regulatory Assets and Liabilities
Regulatory assets	522	496
Pension balancing account
Regulatory Assets and Liabilities
Regulatory assets	3,742	2,322
Other components of net periodic benefit cost
Regulatory Assets and Liabilities
Regulatory assets	811	0
Other regulatory assets
Regulatory Assets and Liabilities
Regulatory assets	$ 738	$ 935