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Regulatory Assets and Liabilities - Schedule of Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands | Sep. 30, 2025 | Dec. 31, 2024
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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

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