Significant Accounting Policies - Additional Information (Details) - USD ($) |
3 Months Ended | 9 Months Ended | |||
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Jun. 30, 2026 |
Jun. 30, 2025 |
Jun. 30, 2026 |
Jun. 30, 2025 |
Sep. 30, 2025 |
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| Summary of Account Policies [Line Items] | |||||
| Restricted cash | $ 112,000 | $ 112,000 | $ 2,953,000 | ||
| Restricted investments | 10,870,000 | 10,870,000 | $ 23,176,000 | ||
| Debt securities, available-for-sale, allowance for credit loss | $ 0 | $ 0 | $ 0 | $ 0 | |
| Number of reportable segments, not disclosed flag | |||||
| Department of Transportation | Revenues | Customer Concentration Risk | |||||
| Summary of Account Policies [Line Items] | |||||
| Concentration risk percentage | 44.70% | 46.10% | 42.00% | 40.80% | |
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- Definition Number Of Reportable Segments, Not Disclosed Flag No definition available.
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- Definition Summary Of Account Policies [Line Items] No definition available.
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- Definition For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount excluding accrued interest, of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount of cash restricted as to withdrawal or usage, classified as current. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition This element represents the noncurrent portion of investments which are not defined as or included in marketable (debt, equity, or other) securities that are pledged or subject to withdrawal restrictions. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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