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Capitalization - Narrative (Details) $ / shares in Units, gal in Millions |  | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
May 12, 2025 USD ($) | Sep. 30, 2025 USD ($) shares | May 31, 2024 USD ($) loan | Sep. 30, 2025 USD ($) $ / shares shares | Jun. 30, 2025 USD ($) shares | Sep. 30, 2025 USD ($) project $ / shares shares gal | Sep. 30, 2024 USD ($) shares | Sep. 30, 2025 USD ($) | Oct. 31, 2025 USD ($) | Dec. 31, 2024 USD ($) | Apr. 30, 2023 shares
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Value of common shares issued |  |  |  | $ 16,992,000 | $ 3,604,000 |  |  |  |  |  |
Number of shares approved to issue and sell (in shares) | shares |  |  |  |  |  |  |  |  |  |  | 1,000,000.0
Total net proceeds from shares issued and sold under agreement |  |  |  |  |  | $ 21,281,000 | $ 740,000 |  |  |  |
Debt drawn down |  |  |  |  |  | 3,603,000 | 592,000 |  |  |  |
Loans Payable | New Jersey SRF |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Borrowing amount |  | $ 300,000,000.0 |  | 300,000,000.0 |  | 300,000,000.0 |  | $ 300,000,000.0 |  |  |
Maximum petitioned borrowing amount approved |  | 260,000,000.0 |  | 260,000,000.0 |  | 260,000,000.0 |  | 260,000,000.0 |  |  |
Loans Payable | September 2024 Delaware SRF | Tidewater |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Borrowing amount |  |  |  |  |  |  | $ 2,200,000 |  |  |  |
Interest rate |  |  |  |  |  |  | 0.00% |  |  |  |
Debt drawn down |  |  |  |  |  |  |  | 1,700,000 |  |  |
Loans Payable | May 2024 Delaware SRF | Tidewater |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Borrowing amount |  |  | $ 5,600,000 |  |  |  |  |  |  |  |
Interest rate |  |  | 2.00% |  |  |  |  |  |  |  |
Debt drawn down |  |  |  |  |  | 900,000 |  |  |  |  |
Number of debt instruments | loan |  |  | 4 |  |  |  |  |  |  |  |
Loans Payable | 2023 Delaware SRF | Tidewater |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt drawn down |  |  |  |  |  | $ 7,200,000 |  |  |  |  |
Number of active construction projects funded by debt instruments | project |  |  |  |  |  | 2 |  |  |  |  |
Carrying amount of debt |  | 8,300,000 |  | 8,300,000 |  | $ 8,300,000 |  | 8,300,000 |  |  |
Size of elevated storage tank (in gallons) | gal |  |  |  |  |  | 1 |  |  |  |  |
Loans Payable | Amortizing Secured Notes And State Revolving Trust Notes |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Carrying amount of debt |  | 230,500,000 |  | 230,500,000 |  | $ 230,500,000 |  | 230,500,000 |  | $ 229,800,000 |
Loans Payable | Construction Advances |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Carrying amount of debt |  | $ 24,100,000 |  | $ 24,100,000 |  | $ 24,100,000 |  | 24,100,000 |  | $ 22,600,000 |
Secured Debt | 5.99% FMBs due 2055 | Subsequent Event |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Borrowing amount |  |  |  |  |  |  |  |  | $ 30,000,000 |  |
Interest rate |  |  |  |  |  |  |  |  | 5.99% |  |
Underwritten Public Offering and/or ATM Offering |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Maximum number of shares petitioned to issue and sell during offering (in shares) | shares |  | 2,500,000 |  |  |  |  |  |  |  |  |
ATM Equity Sales Agreement |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Aggregate gross sales price | $ 110,000,000.0 |  |  |  |  |  |  |  |  |  |
Number of shares issued and sold under agreement (in shares) | shares |  |  |  | 316,786 |  | 380,741 |  |  |  |  |
Weighted average price per share of shares issued and sold under agreement (in dollars per share) | $ / shares |  |  |  | $ 53.47 |  | $ 54.10 |  |  |  |  |
Total net proceeds from shares issued and sold under agreement |  |  |  | $ 16,700,000 |  | $ 20,300,000 |  |  |  |  |
Aggregate gross sales price of shares remaining to be issued under agreement |  | $ 89,400,000 |  | $ 89,400,000 |  | $ 89,400,000 |  | $ 89,400,000 |  |  |
Common Stock |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of common shares issued (in shares) | shares |  |  |  | 317,000 | 64,000 | 12,522 | 13,498 |  |  |  |
Value of common shares issued |  |  |  | $ 16,992,000 | $ 3,604,000 | $ 700,000 | $ 700,000 |  |  |  |

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