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Note 4 - Investments - Investments (Details) - USD ($) $ in Thousands | Jun. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Investments at cost | $ 745,848 | $ 766,774
Investments at fair value | 622,653 | 697,891
Biotechnology Sector [Member] |  |
Investments at cost | 120,283 | 118,221
Investments at fair value | 84,043 | 97,562
Medical Device Sector [Member] |  |
Investments at cost | 239,170 | 213,564
Investments at fair value | 209,087 | 205,634
Communications Sector [Member] |  |
Investments at cost | 517 | 11,711
Investments at fair value | 3,532 | 14,763
Consumer-related Sector [Member] |  |
Investments at cost | 65,352 | 74,421
Investments at fair value | 25,066 | 36,667
Data Storage Sector [Member] |  |
Investments at cost | 417 | 417
Investments at fair value | 330 | 350
Internet and Media Sector [Member] |  |
Investments at cost | 329 | 329
Investments at fair value | 605 | 999
Networking Sector [Member] |  |
Investments at cost | 364 | 10,070
Investments at fair value | 121 | 9,827
Semiconductor Sector [Member] |  |
Investments at cost | 0 | 45
Investments at fair value | 0 | 0
Software Sector [Member] |  |
Investments at cost | 165,371 | 154,040
Investments at fair value | 158,536 | 151,043
Alternative Energy [Member] |  |
Investments at cost | 4,854 | 0
Investments at fair value | 4,845 | 0
Energy Efficiency [Member] |  |
Investments at cost | 9,934 | 9,818
Investments at fair value | 9,828 | 9,712
Other Sustainability Sector [Member] |  |
Investments at cost | 30,449 | 66,151
Investments at fair value | 23,008 | 66,079
Diagnostics Sector [Member] |  |
Investments at cost | 17,350 | 16,704
Investments at fair value | 9,940 | 13,701
Other Healthcare Sector [Member] |  |
Investments at cost | 39,575 | 39,533
Investments at fair value | 42,194 | 40,144
Software, Healthcare Information and Service [Member] |  |
Investments at cost | 51,883 | 51,750
Investments at fair value | 51,518 | 51,410
Debt [Member] |  |
Investments at cost | 636,261 | 678,167
Investments at fair value | 579,171 | 638,779
Warrant [Member] |  |
Investments at cost | 15,565 | 15,956
Investments at fair value | 21,629 | 18,277
Other Debt Obligations [Member] |  |
Investments at cost | 55,924 | 36,709
Investments at fair value | 8,451 | 14,637
Equity Securities [Member] |  |
Investments at cost | 38,098 | 35,942
Investments at fair value | $ 13,402 | $ 26,198

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