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Summary of Significant Accounting Policies (Details) $ in Thousands |  | 1 Months Ended | 3 Months Ended | 9 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Feb. 27, 2024 USD ($) | May 31, 2025 USD ($) shares | Sep. 30, 2025 USD ($) state contract shares | Jun. 30, 2025 USD ($) | Mar. 31, 2025 USD ($) | Sep. 30, 2024 USD ($) shares | Jun. 30, 2024 USD ($) | Mar. 31, 2024 USD ($) | Sep. 30, 2025 USD ($) customer registrant contract state shares | Sep. 30, 2024 USD ($) shares | May 29, 2025 USD ($) | Mar. 13, 2025 USD ($) | Feb. 12, 2025 USD ($) | Dec. 31, 2024 USD ($)
Summary of significant accounting policies |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of customers | customer |  |  |  |  |  |  |  |  | 1,000,000 |  |  |  |  |
Number of states in which entity operates | state |  |  | 10 |  |  |  |  |  | 10 |  |  |  |  |
Property installed by developers and conveyed |  |  |  |  |  |  |  |  | $ 17,514 | $ 4,971 |  |  |  |
Number of registrants filing combined report | registrant |  |  |  |  |  |  |  |  | 2 |  |  |  |  |
Issuance of Common Shares from an at-the-market offering program, net of issuance costs |  |  | $ 14,624 |  | $ 25,648 | $ 26,881 | $ 16,724 | $ 15,584 |  |  |  |  |  |
Sale of stock, maximum consideration on transaction | $ 200,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Agreement term (in years) | 3 years |  |  |  |  |  |  |  |  |  |  |  |  |
Sale of stock, number of shares issued in transaction (in shares) | shares |  |  | 201,212 |  |  | 335,449 |  |  | 535,760 | 791,097 |  |  |  |
Sale of stock, consideration received on transaction |  |  |  |  |  | $ 27,000 |  |  | $ 40,500 | $ 60,000 |  |  |  |
Payments for commissions |  |  | $ 200 |  |  | 400 |  |  | 600 | 900 |  |  |  |
Payments of stock issuance costs |  |  | 100 |  |  | 100 |  |  | 300 | 800 |  |  |  |
Sale of Stock, remaining available for sale |  |  | 68,000 |  |  |  |  |  | $ 68,000 |  |  |  |  |
Debt instrument term (in years) |  |  |  |  |  |  |  |  | 5 years |  |  |  |  |
Incremental expansion of borrowing capacity |  |  | 30,000 |  |  |  |  |  | $ 30,000 |  |  |  |  |
Notes payable to banks |  |  | 119,000 |  |  |  |  |  | 119,000 |  |  |  |  | $ 165,000
Syndicated Revolving Credit Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies |  |  |  |  |  |  |  |  |  |  |  |  |  |
Notes payable to banks |  |  | 119,000 |  |  |  |  |  | 119,000 |  |  |  |  |
GSWC |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property installed by developers and conveyed |  |  |  |  |  |  |  |  | $ 17,514 | 4,971 |  |  |  |
Issuance of Common Shares from an at-the-market program, net of issuance costs (in shares) | shares |  | 3.6500 |  |  |  |  |  |  | 3.6500 |  |  |  |  |
Issuance of Common Shares from an at-the-market offering program, net of issuance costs |  | $ 50,000 |  | $ 50,005 |  |  |  |  | $ 50,000 |  |  |  |  |
Sale of stock, consideration received on transaction |  |  | 14,700 |  |  |  |  |  |  |  |  |  |  |
Incremental expansion of borrowing capacity |  |  | 75,000 |  |  |  |  |  | 75,000 |  |  |  |  |
GSWC | Financing Application |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory rate case filings requested authorization for debt and equity issuance |  |  |  |  |  |  |  |  |  |  |  | $ 750,000 |  |
GSWC | Syndicated Revolving Credit Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies |  |  |  |  |  |  |  |  |  |  |  |  |  |
Notes payable to banks |  |  | 0 |  |  |  |  |  | 0 |  |  |  |  |
GSWC | Unsecured private-placement notes |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of debt |  |  | 100,000 |  |  |  |  |  | $ 100,000 |  | $ 100,000 |  |  |
GSWC | Series A Senior Notes at a coupon rate of 5.65% due May 29, 2037 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of debt |  |  |  |  |  |  |  |  |  |  | $ 75,000 |  |  |
Stated interest rate percentage |  |  |  |  |  |  |  |  |  |  | 5.30% |  |  |
GSWC | Series B Senior Notes at a coupon rate of 5.65% due May 29, 2037 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of debt |  |  |  |  |  |  |  |  |  |  | $ 25,000 |  |  |
Stated interest rate percentage |  |  |  |  |  |  |  |  |  |  | 5.65% |  |  |
GSWC | Water: |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of customers | customer |  |  |  |  |  |  |  |  | 265,000 |  |  |  |  |
GSWC | Water: | San Juan Oak |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies |  |  |  |  |  |  |  |  |  |  |  |  |  |
Service connections | customer |  |  |  |  |  |  |  |  | 1,300 |  |  |  |  |
Property installed by developers and conveyed |  |  |  | $ 10,700 |  |  |  |  |  |  |  |  |  |
BVES |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to affiliate for corporate office administrative and general costs |  |  | 800 |  |  | 700 |  |  | $ 2,700 | 2,400 |  |  |  |
Face amount of debt |  |  |  |  |  |  |  |  |  |  |  |  | $ 50,000 |
Maximum borrowing capacity on line of credit |  |  | 65,000 |  |  |  |  |  | 65,000 |  |  |  |  |
BVES | Syndicated Revolving Credit Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies |  |  |  |  |  |  |  |  |  |  |  |  |  |
Notes payable to banks |  |  | 5,000 |  |  |  |  |  | 5,000 |  |  |  |  |
BVES | Unsecured private-placement notes |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of debt |  |  | 50,000 |  |  |  |  |  | $ 50,000 |  |  |  |  |
BVES | Electric: |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of customers | customer |  |  |  |  |  |  |  |  | 25,000 |  |  |  |  |
ASUS |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to affiliate for corporate office administrative and general costs |  |  | $ 1,200 |  |  | $ 1,200 |  |  | $ 4,000 | $ 4,000 |  |  |  |
Bay State Utility Service LLC (" BSUS") |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of contracts with 15 year contract | contract |  |  | 1 |  |  |  |  |  | 1 |  |  |  |  |
Bay State Utility Service LLC (" BSUS") | Contracted services: |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period of fixed price contracts to operate and maintain water systems at various military bases |  |  |  |  |  |  |  |  | 15 years |  |  |  |  |
Maximum | Syndicated Revolving Credit Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies |  |  |  |  |  |  |  |  |  |  |  |  |  |
Current borrowing capacity |  |  | $ 195,000 |  |  |  |  |  | $ 195,000 |  |  |  |  |
Maximum | GSWC | Syndicated Revolving Credit Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies |  |  |  |  |  |  |  |  |  |  |  |  |  |
Current borrowing capacity |  |  | 200,000 |  |  |  |  |  | $ 200,000 |  |  |  |  |
Maximum | ASUS |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period of fixed price contracts to operate and maintain water systems at various military bases |  |  |  |  |  |  |  |  | 50 years |  |  |  |  |
Minimum | Syndicated Revolving Credit Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of significant accounting policies |  |  |  |  |  |  |  |  |  |  |  |  |  |
Current borrowing capacity |  |  | $ 165,000 |  |  |  |  |  | $ 165,000 |  |  |  |  |

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