Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 382,484	$ 353,569
Total Regulatory Liabilities	200,657	211,275
Short-term portion of the regulatory assets	33,437	42,394
Short-term portion of the regulatory liabilities	6,887	12,213
Property-related temporary differences (tax benefits flowed through to customers)
Regulatory Assets and Liabilities
Total Regulatory Liabilities	180,207	180,205
Health care balancing account
Regulatory Assets and Liabilities
Total Regulatory Liabilities	4,315	3,516
Conservation program
Regulatory Assets and Liabilities
Total Regulatory Liabilities	5,659	6,880
Net WRAM and MCBA long-term payable
Regulatory Assets and Liabilities
Total Regulatory Liabilities	67	222
Tax accounting memorandum account
Regulatory Assets and Liabilities
Total Regulatory Liabilities	785	5,039
Cost of capital memorandum account
Regulatory Assets and Liabilities
Total Regulatory Liabilities	148	2,834
1,2,3 trichloropropane settlement proceeds
Regulatory Assets and Liabilities
Total Regulatory Liabilities	9,204	12,142
Other regulatory liabilities
Regulatory Assets and Liabilities
Total Regulatory Liabilities	272	437
Pension and retiree group health
Regulatory Assets and Liabilities
Total Regulatory Assets	156,453	156,947
Property-related temporary differences (tax benefits flowed through to customers)
Regulatory Assets and Liabilities
Total Regulatory Assets	100,943	99,376
Other accrued benefits
Regulatory Assets and Liabilities
Total Regulatory Assets	21,183	20,588
Net WRAM and MCBA long-term accounts receivable
Regulatory Assets and Liabilities
Total Regulatory Assets	30,454	17,134
Asset retirement obligations, net
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 19,619	18,197
Interim rates long-term accounts receivable
Regulatory Assets and Liabilities
Recovery Period	1 year
Total Regulatory Assets	$ 4,642	4,642
Tank coating
Regulatory Assets and Liabilities
Recovery Period	10 years
Total Regulatory Assets	$ 13,745	11,196
Recoverable property losses
Regulatory Assets and Liabilities
Recovery Period	10 years
Total Regulatory Assets	$ 5,539	1,275
Pension balancing account
Regulatory Assets and Liabilities
Recovery Period	1 year
Total Regulatory Assets	$ 20,158	16,494
Other components of net periodic benefit cost
Regulatory Assets and Liabilities
Total Regulatory Assets	4,641	3,221
Other regulatory assets
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 5,107	$ 4,499
Minimum | Net WRAM and MCBA long-term accounts receivable
Regulatory Assets and Liabilities
Recovery Period	1 year
Maximum | Net WRAM and MCBA long-term accounts receivable
Regulatory Assets and Liabilities
Recovery Period	2 years