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Note 4 - Investments - Investments (Details) - USD ($) $ in Thousands | Mar. 31, 2024 | Dec. 31, 2023
--- | --- | ---
Investments at cost | $ 765,173 | $ 759,182
Investments at fair value | 711,116 | 709,085
Biotechnology Sector [Member] |  |
Investments at cost | 142,108 | 145,544
Investments at fair value | 124,741 | 117,781
Medical Device Sector [Member] |  |
Investments at cost | 164,060 | 147,064
Investments at fair value | 161,155 | 145,019
Communications Sector [Member] |  |
Investments at cost | 17,327 | 19,192
Investments at fair value | 20,185 | 22,188
Consumer-related Sector [Member] |  |
Investments at cost | 105,165 | 105,669
Investments at fair value | 99,876 | 101,327
Data Storage Sector [Member] |  |
Investments at cost | 416 | 417
Investments at fair value | 426 | 418
Internet and Media Sector [Member] |  |
Investments at cost | 328 | 329
Investments at fair value | 1,592 | 1,582
Networking Sector [Member] |  |
Investments at cost | 3,231 | 5,451
Investments at fair value | 3,091 | 5,297
Power Management Sector [Member] |  |
Investments at cost | 1,585 | 1,585
Investments at fair value | 2,700 | 2,700
Semiconductor Sector [Member] |  |
Investments at cost | 45 | 45
Investments at fair value | 0 | 0
Software Sector [Member] |  |
Investments at cost | 159,094 | 164,133
Investments at fair value | 154,908 | 160,749
Energy Efficiency [Member] |  |
Investments at cost | 111 | 111
Investments at fair value | 8 | 13
Other Sustainability Sector [Member] |  |
Investments at cost | 100,854 | 98,906
Investments at fair value | 71,060 | 80,370
Diagnostics Sector [Member] |  |
Investments at cost | 19,759 | 19,735
Investments at fair value | 19,729 | 19,701
Other Healthcare Sector [Member] |  |
Investments at cost | 102 | 102
Investments at fair value | 949 | 1,366
Software, Healthcare Information and Service [Member] |  |
Investments at cost | 50,988 | 50,899
Investments at fair value | 50,696 | 50,574
Debt [Member] |  |
Investments at cost | 719,500 | 721,231
Investments at fair value | 670,773 | 670,172
Warrant [Member] |  |
Investments at cost | 16,636 | 16,526
Investments at fair value | 23,928 | 24,594
Other Debt Obligations [Member] |  |
Investments at cost | 13,844 | 6,982
Investments at fair value | 9,192 | 6,430
Equity Securities [Member] |  |
Investments at cost | 15,193 | 14,443
Investments at fair value | $ 7,223 | $ 7,889

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