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Note 4 - Investments - Investments (Details) - USD ($) $ in Thousands | Dec. 31, 2024 | Dec. 31, 2023
--- | --- | ---
Investments at cost | $ 766,774 | $ 759,182
Investments at fair value | 697,891 | 709,085
Biotechnology Sector [Member] |  |
Investments at cost | 118,221 | 145,544
Investments at fair value | 97,562 | 117,781
Medical Device Sector [Member] |  |
Investments at cost | 213,564 | 147,064
Investments at fair value | 205,634 | 145,019
Communications Sector [Member] |  |
Investments at cost | 11,711 | 19,192
Investments at fair value | 14,763 | 22,188
Consumer-related Sector [Member] |  |
Investments at cost | 74,421 | 105,669
Investments at fair value | 36,667 | 101,327
Data Storage Sector [Member] |  |
Investments at cost | 417 | 417
Investments at fair value | 350 | 418
Internet and Media Sector [Member] |  |
Investments at cost | 329 | 329
Investments at fair value | 999 | 1,582
Networking Sector [Member] |  |
Investments at cost | 10,070 | 5,451
Investments at fair value | 9,827 | 5,297
Power Management Sector [Member] |  |
Investments at cost | 0 | 1,585
Investments at fair value | 0 | 2,700
Semiconductor Sector [Member] |  |
Investments at cost | 45 | 45
Investments at fair value | 0 | 0
Software Sector [Member] |  |
Investments at cost | 154,040 | 164,133
Investments at fair value | 151,043 | 160,749
Energy Efficiency [Member] |  |
Investments at cost | 9,818 | 111
Investments at fair value | 9,712 | 13
Other Sustainability Sector [Member] |  |
Investments at cost | 66,151 | 98,906
Investments at fair value | 66,079 | 80,370
Diagnostics Sector [Member] |  |
Investments at cost | 16,704 | 19,735
Investments at fair value | 13,701 | 19,701
Other Healthcare Sector [Member] |  |
Investments at cost | 39,533 | 102
Investments at fair value | 40,144 | 1,366
Software, Healthcare Information and Service [Member] |  |
Investments at cost | 51,750 | 50,899
Investments at fair value | 51,410 | 50,574
Debt [Member] |  |
Investments at cost | 678,167 | 721,231
Investments at fair value | 638,779 | 670,172
Warrant [Member] |  |
Investments at cost | 15,956 | 16,526
Investments at fair value | 18,277 | 24,594
Other Debt Obligations [Member] |  |
Investments at cost | 36,709 | 6,982
Investments at fair value | 14,637 | 6,430
Equity Securities [Member] |  |
Investments at cost | 35,942 | 14,443
Investments at fair value | $ 26,198 | $ 7,889

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