Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Regulatory Assets and Liabilities
Regulatory assets	$ 405,297	$ 401,147
Regulatory liabilities	192,755	179,706
Short-term portion of the regulatory assets	33,257	36,783
Short-term portion of the regulatory liabilities	56,317	59,303
Property-related temporary differences (tax benefits flowed through to customers)
Regulatory Assets and Liabilities
Regulatory liabilities	168,384	168,343
Health care balancing account
Regulatory Assets and Liabilities
Regulatory liabilities	11,127	7,749
Conservation program
Regulatory Assets and Liabilities
Regulatory liabilities	4,531	2,273
Pension balancing account
Regulatory Assets and Liabilities
Regulatory liabilities	13	364
Net WRAM and MCBA long-term payable
Regulatory Assets and Liabilities
Regulatory liabilities	938	513
Tax accounting memorandum account
Regulatory Assets and Liabilities
Regulatory liabilities	4,767	0
Cost of capital memorandum account
Regulatory Assets and Liabilities
Regulatory liabilities	2,834	0
Other regulatory liabilities
Regulatory Assets and Liabilities
Regulatory liabilities	161	464
Pension and retiree group health
Regulatory Assets and Liabilities
Regulatory assets	213,920	214,249
Property-related temporary differences (tax benefits flowed through to customers)
Regulatory Assets and Liabilities
Regulatory assets	87,988	87,323
Other accrued benefits
Regulatory Assets and Liabilities
Regulatory assets	28,741	28,251
Net WRAM and MCBA long-term accounts receivable
Regulatory Assets and Liabilities
Regulatory assets	32,892	34,879
Asset retirement obligations, net
Regulatory Assets and Liabilities
Regulatory assets	17,824	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	11,467	10,998
Health care balancing account
Regulatory Assets and Liabilities
Regulatory assets	442	496
Pension balancing account
Regulatory Assets and Liabilities
Regulatory assets	5,136	2,322
Other components of net periodic benefit cost
Regulatory Assets and Liabilities
Regulatory assets	1,754	0
Other regulatory assets
Regulatory Assets and Liabilities
Regulatory assets	$ 565	$ 935