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Note 4 - Investments - Investments (Details) - USD ($) $ in Thousands | Sep. 30, 2023 | Dec. 31, 2022
--- | --- | ---
Investments at cost | $ 754,814 | $ 721,248
Investments at fair value | 729,053 | 720,026
Biotechnology Sector [Member] |  |
Investments at cost | 158,953 | 193,372
Investments at fair value | 139,935 | 195,006
Medical Device Sector [Member] |  |
Investments at cost | 140,172 | 132,803
Investments at fair value | 139,039 | 135,960
Communications Sector [Member] |  |
Investments at cost | 21,057 | 22,892
Investments at fair value | 24,317 | 26,176
Consumer-related Sector [Member] |  |
Investments at cost | 110,245 | 121,961
Investments at fair value | 106,559 | 114,050
Data Storage Sector [Member] |  |
Investments at cost | 417 | 476
Investments at fair value | 1,070 | 1,316
Internet and Media Sector [Member] |  |
Investments at cost | 329 | 329
Investments at fair value | 1,615 | 1,159
Networking Sector [Member] |  |
Investments at cost | 6,671 | 11,831
Investments at fair value | 6,558 | 11,710
Power Management Sector [Member] |  |
Investments at cost | 1,585 | 1,585
Investments at fair value | 2,901 | 2,610
Semiconductor Sector [Member] |  |
Investments at cost | 56 | 56
Investments at fair value | 0 | 0
Software Sector [Member] |  |
Investments at cost | 164,903 | 120,157
Investments at fair value | 161,258 | 118,716
Energy Efficiency [Member] |  |
Investments at cost | 111 | 8
Investments at fair value | 36 | 27
Other Sustainability Sector [Member] |  |
Investments at cost | 89,395 | 84,633
Investments at fair value | 83,476 | 85,524
Diagnostics Sector [Member] |  |
Investments at cost | 9,971 | 9,851
Investments at fair value | 9,939 | 9,858
Other Healthcare Sector [Member] |  |
Investments at cost | 102 | 7,559
Investments at fair value | 1,379 | 3,870
Software, Healthcare Information and Service [Member] |  |
Investments at cost | 50,847 | 13,735
Investments at fair value | 50,971 | 14,044
Debt [Member] |  |
Investments at cost | 716,655 | 701,074
Investments at fair value | 679,838 | 686,458
Warrant [Member] |  |
Investments at cost | 15,783 | 14,790
Investments at fair value | 26,189 | 29,712
Other Debt Obligations [Member] |  |
Investments at cost | 7,354 | 1,200
Investments at fair value | 7,254 | 1,300
Equity Securities [Member] |  |
Investments at cost | 15,022 | 4,184
Investments at fair value | $ 15,772 | $ 2,556

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