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Note 4 - Investments - Investments (Details) - USD ($) $ in Thousands | Jun. 30, 2026 | Dec. 31, 2025
--- | --- | ---
Investments at cost | $ 777,867 | $ 705,269
Investments at fair value | 676,711 | 647,244
Biotechnology Sector [Member] |  |
Investments at cost | 117,812 | 94,280
Investments at fair value | 86,231 | 61,829
Medical Device Sector [Member] |  |
Investments at cost | 230,456 | 227,893
Investments at fair value | 232,913 | 222,485
Communications Sector [Member] |  |
Investments at cost | 6,286 | 522
Investments at fair value | 7,459 | 3,142
Consumer-related Sector [Member] |  |
Investments at cost | 30,840 | 31,204
Investments at fair value | 19,800 | 21,846
Data Storage Sector [Member] |  |
Investments at cost | 417 | 417
Investments at fair value | 197 | 230
Internet and Media Sector [Member] |  |
Investments at cost | 329 | 329
Investments at fair value | 78 | 151
Networking Sector [Member] |  |
Investments at cost | 364 | 364
Investments at fair value | 0 | 0
Software Sector [Member] |  |
Investments at cost | 237,700 | 199,608
Investments at fair value | 228,691 | 190,911
Alternative Energy [Member] |  |
Investments at cost | 0 | 4,914
Investments at fair value | 0 | 4,905
Energy Efficiency [Member] |  |
Investments at cost | 125 | 125
Investments at fair value | 15 | 9
Other Sustainability Sector [Member] |  |
Investments at cost | 57,406 | 50,321
Investments at fair value | 18,223 | 49,315
Diagnostics Sector [Member] |  |
Investments at cost | 12,001 | 11,553
Investments at fair value | 10,560 | 11,369
Other Healthcare Sector [Member] |  |
Investments at cost | 38,889 | 38,668
Investments at fair value | 30,041 | 34,508
Software, Healthcare Information and Service [Member] |  |
Investments at cost | 45,027 | 45,071
Investments at fair value | 42,288 | 46,544
Joint Venture Investment Funds [Member] | RoHo Capital Opportunity LLC [Member] |  |
Investments at cost | 215 | 0
Investments at fair value | 215 | 0
Debt [Member] |  |
Investments at cost | 682,425 | 602,488
Investments at fair value | 647,999 | 596,025
Warrant [Member] |  |
Investments at cost | 15,155 | 14,868
Investments at fair value | 16,703 | 16,648
Other Debt Obligations [Member] |  |
Investments at cost | 37,962 | 45,258
Investments at fair value | 4,037 | 3,444
Equity Securities [Member] |  |
Investments at cost | 42,110 | 42,655
Investments at fair value | 7,757 | 31,127
Joint Venture Investment Funds [Member] |  |
Investments at cost | 215 | 0
Investments at fair value | $ 215 | $ 0

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