Regulatory Assets and Liabilities - Schedule of Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 291,577	$ 285,692
Total Regulatory Liabilities	181,827	180,428
Future tax benefits due to customers
Regulatory Assets and Liabilities
Total Regulatory Liabilities	134,378	135,027
Retiree group health
Regulatory Assets and Liabilities
Total Regulatory Liabilities	27,294	27,294
HCBA
Regulatory Assets and Liabilities
Total Regulatory Liabilities	11,355	9,687
CEBA
Regulatory Assets and Liabilities
Total Regulatory Liabilities	7,395	7,206
Net WRAM and MCBA long-term payable
Regulatory Assets and Liabilities
Total Regulatory Liabilities	262	143
Other regulatory liabilities
Regulatory Assets and Liabilities
Total Regulatory Liabilities	1,143	1,071
Pension and retiree group health
Regulatory Assets and Liabilities
Total Regulatory Assets	17,443	17,607
Future tax benefits due to customers
Regulatory Assets and Liabilities
Total Regulatory Assets	130,565	130,565
Other accrued benefits
Regulatory Assets and Liabilities
Total Regulatory Assets	24,644	23,280
Net WRAM and MCBA long-term accounts receivable
Regulatory Assets and Liabilities
Total Regulatory Assets	39,013	29,789
Asset retirement obligations, net
Regulatory Assets and Liabilities
Total Regulatory Assets	23,467	22,935
Interim rates memorandum account (IRMA) long-term accounts receivable
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 7,972	9,032
Tank coating
Regulatory Assets and Liabilities
Recovery Period	10 years
Total Regulatory Assets	$ 14,347	13,680
Recoverable property losses
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 3,666	3,843
PCBA
Regulatory Assets and Liabilities
Recovery Period	1 year
Total Regulatory Assets	$ 20,877	21,500
Other components of net periodic benefit cost
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 2,091	3,342
General district balancing account receivable
Regulatory Assets and Liabilities
Recovery Period	1 year
Total Regulatory Assets	$ 618	568
Customer assistance program (CAP) and Rate support fund (RSF) accounts receivable
Regulatory Assets and Liabilities
Recovery Period	1 year
Total Regulatory Assets	$ 3,392	5,991
Other regulatory assets
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 3,482	$ 3,560
Minimum | Net WRAM and MCBA long-term accounts receivable
Regulatory Assets and Liabilities
Recovery Period	1 year
Minimum | Interim rates memorandum account (IRMA) 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
Maximum | Interim rates memorandum account (IRMA) long-term accounts receivable
Regulatory Assets and Liabilities
Recovery Period	3 years