Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 328,336	$ 325,376
Total Regulatory Liabilities	183,597	180,718
Short-term portion of the regulatory assets	97,820	96,241
Short-term portion of the regulatory liabilities	34,215	34,636
Future tax benefits due to customers
Regulatory Assets and Liabilities
Total Regulatory Liabilities	151,088	151,011
Retiree group health
Regulatory Assets and Liabilities
Total Regulatory Liabilities	18,472	18,472
HCBA
Regulatory Assets and Liabilities
Total Regulatory Liabilities	7,165	5,320
CEBA
Regulatory Assets and Liabilities
Total Regulatory Liabilities	4,313	3,837
Net WRAM and MCBA long-term payable
Regulatory Assets and Liabilities
Total Regulatory Liabilities	1,397	479
Other regulatory liabilities
Regulatory Assets and Liabilities
Total Regulatory Liabilities	1,162	1,599
Pension and retiree group health
Regulatory Assets and Liabilities
Total Regulatory Assets	59,424	59,588
Future tax benefits due to customers
Regulatory Assets and Liabilities
Total Regulatory Assets	120,590	120,365
Other accrued benefits
Regulatory Assets and Liabilities
Total Regulatory Assets	22,192	21,692
Net WRAM and MCBA long-term accounts receivable
Regulatory Assets and Liabilities
Total Regulatory Assets	38,676	33,136
Asset retirement obligations, net
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 21,624	21,110
IRMA long-term accounts receivable
Regulatory Assets and Liabilities
Recovery Period	1 year
Total Regulatory Assets	$ 10,962	14,705
Tank coating
Regulatory Assets and Liabilities
Recovery Period	10 years
Total Regulatory Assets	$ 13,777	14,018
Recoverable property losses
Regulatory Assets and Liabilities
Recovery Period	9 years
Total Regulatory Assets	$ 4,361	4,531
PCBA
Regulatory Assets and Liabilities
Recovery Period	1 year
Total Regulatory Assets	$ 21,210	19,647
Other components of net periodic benefit cost
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 5,988	6,736
General district balancing account receivable
Regulatory Assets and Liabilities
Recovery Period	1 year
Total Regulatory Assets	$ 724	1,830
Low-income rate assistance (LIRA) and Rate support fund (RSF) accounts receivable
Regulatory Assets and Liabilities
Recovery Period	1 year
Total Regulatory Assets	$ 6,202	5,310
Other regulatory assets
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 2,606	$ 2,708
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