Regulatory Assets and Liabilities - Schedule of Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Assets	$ 326,519	$ 357,406
Total Regulatory Liabilities	870,620	814,551
Cost of removal
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Liabilities	514,145	483,108
Pension and retiree group health
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Liabilities	173,593	174,708
Future tax benefits due to customers
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Liabilities	104,154	106,184
PFAS settlement proceeds
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Liabilities	24,000	0
Other components of net periodic benefit cost
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Liabilities	22,812	18,287
Pension Cost Balancing Account
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Liabilities	17,009	14,143
Health Cost Balancing Account
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Liabilities	4,264	3,630
Net WRAM and MCBA long-term payable
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Liabilities	3,103	3,064
Conservation Expense Balancing Account
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Liabilities	2,909	3,294
Incremental Cost Balancing Accounts (ICBA)
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Liabilities	2,548	6,003
Other regulatory liabilities
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Liabilities	2,083	2,130
Property-related temporary differences (tax benefits flowed through to customers)
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Assets	178,279	178,279
Asset retirement obligations, net
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Assets	31,051	28,883
Other accrued benefits
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Assets	26,756	25,439
IRMA long-term accounts receivable
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Assets	25,233	46,278
Tank coating
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Assets	19,527	21,477
MWRAM long-term regulatory asset
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Assets	$ 13,570	16,353
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
General District Balancing Account receivable
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Assets	$ 9,724	9,393
Incremental Cost Balancing Accounts (ICBA)
Regulatory Assets and Liabilities [Line Items]
Recovery Period	1 year
Total Regulatory Assets	$ 4,608	8,251
Customer Assistance Program and Rate Support Fund accounts receivable
Regulatory Assets and Liabilities [Line Items]
Recovery Period	1 year
Total Regulatory Assets	$ 4,423	9,910
Net WRAM and Modified Cost Balancing Account (MCBA) long-term accounts receivable
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Assets	3,776	3,633
Recoverable property losses
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Assets	2,131	2,633
Other regulatory assets
Regulatory Assets and Liabilities [Line Items]
Total Regulatory Assets	$ 7,441	$ 6,877