Note 4 - Investments - Securities in a Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands |
Sep. 30, 2023 |
Sep. 30, 2022 |
|---|---|---|
| Fair value unrealized loss, less than 12 months | $ 113,153 | $ 6,345 |
| Gross unrealized loss, less than 12 months | 131 | 176 |
| Fair value unrealized loss, greater than 12 months | 23,476 | 22,204 |
| Gross unrealized loss, greater than 12 months | 755 | 1,414 |
| US Treasury Securities [Member] | ||
| Fair value unrealized loss, less than 12 months | 112,908 | 0 |
| Gross unrealized loss, less than 12 months | 131 | 0 |
| Fair value unrealized loss, greater than 12 months | 15,606 | 15,093 |
| Gross unrealized loss, greater than 12 months | 608 | 1,085 |
| Certificates of Deposit [Member] | ||
| Fair value unrealized loss, less than 12 months | 245 | 6,345 |
| Gross unrealized loss, less than 12 months | 0 | 176 |
| Fair value unrealized loss, greater than 12 months | 7,870 | 7,111 |
| Gross unrealized loss, greater than 12 months | $ 147 | $ 329 |
| 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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- 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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- 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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