Regulatory Assets and Liabilities - Schedule of Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Assets	$ 341,684	$ 339,865
Total Regulatory Liabilities	915,692	929,814
Cost of removal
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Liabilities	533,773	523,813
Pension and retiree group health
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Liabilities	218,412	219,133
Future tax benefits due to customers
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Liabilities	103,085	103,662
Other components of net periodic benefit cost
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Liabilities	26,141	24,248
PFAS settlement proceeds
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Liabilities	19,867	25,193
Pension Balancing Account [Member]
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Liabilities	4,379	17,837
Net WRAM and MCBA long-term payable
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Liabilities	3,130	3,117
Incremental Cost Balancing Accounts (ICBA)
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Liabilities	3,018	2,144
Conservation Expense Balancing Account
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Liabilities	1,277	5,202
Health Cost Balancing Account
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Liabilities	1,019	4,149
Other regulatory liabilities
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Liabilities	1,591	1,316
Property-related temporary differences (tax benefits flowed through to customers)
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Assets	199,465	199,465
Asset retirement obligations, net
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Assets	30,822	30,073
Other accrued benefits
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Assets	28,759	26,263
MWRAM long-term regulatory asset
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Assets	$ 24,283	12,876
MWRAM long-term regulatory asset | Minimum
Regulatory Assets and Liabilities [Line Items]
Recovery Period	1 year
MWRAM long-term regulatory asset | Maximum
Regulatory Assets and Liabilities [Line Items]
Recovery Period	2 years
Interim Rates Memorandum Account (IRMA) long-term accounts receivable
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Assets	$ 19,934	22,077
Tank coating
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Assets	$ 18,814	19,495
Incremental Cost Balancing Accounts (ICBA)
Regulatory Assets and Liabilities [Line Items]
Recovery Period	1 year
Total Regulatory Assets	$ 4,350	4,722
Net WRAM and Modified Cost Balancing Account (MCBA) long-term accounts receivable
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Assets	3,965	4,078
Recoverable property losses
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Assets	1,911	2,051
General District Balancing Account receivable
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Assets	$ 1,720	9,844
Customer Assistance Program and Rate Support Fund accounts receivable
Regulatory Assets and Liabilities [Line Items]
Recovery Period	1 year
Total Regulatory Assets	$ 1,683	2,651
Other regulatory assets
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Assets	$ 5,978	$ 6,270