Note 4 - Investments - Securities in a Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands |
Dec. 31, 2023 |
Sep. 30, 2023 |
|---|---|---|
| Fair value unrealized loss, less than 12 months | $ 38,452 | $ 113,153 |
| Gross unrealized loss, less than 12 months | 50 | 131 |
| Fair value unrealized loss, greater than 12 months | 10,664 | 23,476 |
| Gross unrealized loss, greater than 12 months | 509 | 755 |
| US Treasury Securities [Member] | ||
| Fair value unrealized loss, less than 12 months | 38,207 | 112,908 |
| Gross unrealized loss, less than 12 months | 50 | 131 |
| Fair value unrealized loss, greater than 12 months | 6,280 | 15,606 |
| Gross unrealized loss, greater than 12 months | 444 | 608 |
| Certificates of Deposit [Member] | ||
| Fair value unrealized loss, less than 12 months | 245 | 245 |
| Gross unrealized loss, less than 12 months | 0 | 0 |
| Fair value unrealized loss, greater than 12 months | 4,384 | 7,870 |
| Gross unrealized loss, greater than 12 months | $ 65 | $ 147 |
| 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
|
| 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
|
| 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
|
| 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
|
| X | ||||||||||
- Details
|
| X | ||||||||||
- Details
|