Note 4 - Investments - Securities in a Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands |
Mar. 31, 2026 |
Sep. 30, 2025 |
|---|---|---|
| Fair value unrealized loss, less than 12 months | $ 76,044 | $ 40,330 |
| Gross unrealized loss, less than 12 months | (238) | (36) |
| Fair value unrealized loss, greater than 12 months | 3,034 | 24,623 |
| Gross unrealized loss, greater than 12 months | (12) | (73) |
| US Treasury Securities [Member] | ||
| Fair value unrealized loss, less than 12 months | 76,044 | 40,330 |
| Gross unrealized loss, less than 12 months | (238) | (36) |
| Fair value unrealized loss, greater than 12 months | 2,788 | 24,380 |
| Gross unrealized loss, greater than 12 months | (10) | (68) |
| Certificates of Deposit [Member] | ||
| Fair value unrealized loss, less than 12 months | 0 | 0 |
| Gross unrealized loss, less than 12 months | 0 | 0 |
| Fair value unrealized loss, greater than 12 months | 246 | 243 |
| Gross unrealized loss, greater than 12 months | $ (2) | $ (5) |
| X | ||||||||||
- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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| X | ||||||||||
- Definition Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset. Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
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| X | ||||||||||
- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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| X | ||||||||||
- Definition Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset. Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
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