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Note 4 - Investments - Available-for-sale Investments (Details) - USD ($) $ in Thousands | Mar. 31, 2025 | Sep. 30, 2024
--- | --- | ---
Fair value | $ 124,498 | $ 139,330
Short-term US Treasury Securities [Member] |  |
Amortized cost | 83,110 | 113,987
Unrealized gains | 133 | 382
Unrealized losses | (101) | (45)
Fair value | 83,142 | 114,324
Short-term Certificates of Deposit [Member] |  |
Amortized cost |  | 500
Unrealized gains |  | 1
Unrealized losses |  | 0
Fair value |  | 501
Short-term Investment [Member] |  |
Amortized cost | 83,110 | 114,487
Unrealized gains | 133 | 383
Unrealized losses | (101) | (45)
Fair value | 83,142 | 114,825
US Treasury Securities [Member] |  |
Amortized cost |  | 24,514
Unrealized gains |  | 0
Unrealized losses |  | (245)
Fair value |  | 24,269
Long-term US Treasury Securities [Member] |  |
Amortized cost | 41,151 |
Unrealized gains | 64 |
Unrealized losses | (98) |
Fair value | 41,117 |
Long-term Certificates of Deposit [Member] |  |
Amortized cost | 248 | 248
Unrealized gains | 0 | 0
Unrealized losses | (9) | (12)
Fair value | 239 | 236
Long-term Investment [Member] |  |
Amortized cost | 41,399 | 24,762
Unrealized gains | 64 | 0
Unrealized losses | (107) | (257)
Fair value | $ 41,356 | $ 24,505

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