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Note 5 - Transactions With Affiliated Companies - Investments in Controlled Affiliated Companies (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Investments, fair value |  | $ 720,026 |  |
Net unrealized appreciation (depreciation) on investments |  | (48,780) | $ (5,552) | $ 3,205
Net realized gain (loss) on investments |  | (29,702) | (9,484) | (3,248)
Investments, fair value |  | 709,085 | 720,026 |
Interest Income, Operating, Paid in Kind |  | 8,433 | (0) | 0
Investments, fair value |  | (709,085) | (720,026) |
Investment, Affiliated Issuer, Noncontrolled [Member] |  |  |  |
Investments, fair value |  | 0 | 0 |
Purchases |  | 11 | 0 |
Reductions |  | (11,000) | (30) |
Transfers in/(out) at fair value |  | 38,599 | 0 |
Discount accretion |  | 35 | 0 |
Net unrealized appreciation (depreciation) on investments |  | (26,513) | 0 | (848)
Net realized gain (loss) on investments |  | 0 | 30 | (390)
Investments, fair value |  | 1,132 | 0 | 0
Interest income |  | 1,245 | 0 | 252
Transfers in/(out) at fair value |  | 38,599 | 0 |
Investments, fair value |  | (1,132) | 0 | 0
Investment, Affiliated Issuer, Noncontrolled [Member] | MVI (ABC) LLC fka StereoVision, Inc [Member] |  |  |  |
Investments, fair value |  | 0 | 0 |
Purchases |  |  | 0 |
Reductions |  |  | (30) |
Transfers in/(out) at fair value |  |  | 0 |
Discount accretion |  |  | 0 |
Net unrealized appreciation (depreciation) on investments |  |  | 0 |
Net realized gain (loss) on investments |  |  | 30 |
Investments, fair value |  |  | 0 | 0
Interest income |  |  | 0 |
Transfers in/(out) at fair value |  |  | 0 |
Investments, fair value |  |  | 0 | 0
Investment, Affiliated Issuer, Noncontrolled [Member] | Aulea Medical, Inc. [Member] |  |  |  |
Investments, fair value |  | 0 |  |
Purchases |  | 0 |  |
Reductions |  | 0 |  |
Transfers in/(out) at fair value |  | 0 |  |
Discount accretion |  | 0 |  |
Net unrealized appreciation (depreciation) on investments |  | 0 |  |
Net realized gain (loss) on investments |  | 0 |  |
Investments, fair value |  | 0 | 0 |
Interest income |  | 0 |  |
Transfers in/(out) at fair value |  | 0 |  |
Investments, fair value |  | 0 | 0 |
Investment, Affiliated Issuer, Noncontrolled [Member] | Cadrenal Therapeutics, Inc. [Member] |  |  |  |
Investments, fair value | [1] | 0 |  |
Purchases | [1] | 0 |  |
Reductions | [1] | 0 |  |
Transfers in/(out) at fair value | [1] | (906) |  |
Discount accretion | [1] | 0 |  |
Net unrealized appreciation (depreciation) on investments | [1] | 906 |  |
Net realized gain (loss) on investments | [1] | 0 |  |
Investments, fair value | [1] | 0 | 0 |
Interest income | [1] | 0 |  |
Transfers in/(out) at fair value | [1] | (906) |  |
Investments, fair value | [1] | 0 | 0 |
Investment, Affiliated Issuer, Noncontrolled [Member] | Evelo Biosciences, Inc. [Member] | Investment One [Member] |  |  |  |
Investments, fair value |  | 0 |  |
Purchases |  | 0 |  |
Reductions |  | (2,443) |  |
Transfers in/(out) at fair value |  | 7,663 |  |
Discount accretion |  | 8 |  |
Net unrealized appreciation (depreciation) on investments |  | (5,006) |  |
Net realized gain (loss) on investments |  | 0 |  |
Investments, fair value |  | 222 | 0 |
Interest income |  | 277 |  |
Transfers in/(out) at fair value |  | 7,663 |  |
Investments, fair value |  | (222) | 0 |
Investment, Affiliated Issuer, Noncontrolled [Member] | Evelo Biosciences, Inc. [Member] | Investment Two [Member] |  |  |  |
Investments, fair value |  | 0 |  |
Purchases |  | 11 |  |
Reductions |  | (3,667) |  |
Transfers in/(out) at fair value |  | 11,509 |  |
Discount accretion |  | 11 |  |
Net unrealized appreciation (depreciation) on investments |  | (7,528) |  |
Net realized gain (loss) on investments |  | 0 |  |
Investments, fair value |  | 336 | 0 |
Interest income |  | 414 |  |
Transfers in/(out) at fair value |  | 11,509 |  |
Investments, fair value |  | (336) | 0 |
Investment, Affiliated Issuer, Noncontrolled [Member] | Evelo Biosciences, Inc. [Member] | Investment Three [Member] |  |  |  |
Investments, fair value |  | 0 |  |
Purchases |  | 0 |  |
Reductions |  | (1,467) |  |
Transfers in/(out) at fair value |  | 4,601 |  |
Discount accretion |  | 5 |  |
Net unrealized appreciation (depreciation) on investments |  | (3,006) |  |
Net realized gain (loss) on investments |  | 0 |  |
Investments, fair value |  | 133 | 0 |
Interest income |  | 166 |  |
Transfers in/(out) at fair value |  | 4,601 |  |
Investments, fair value |  | (133) | 0 |
Investment, Affiliated Issuer, Noncontrolled [Member] | Evelo Biosciences, Inc. [Member] | Investment Four [Member] |  |  |  |
Investments, fair value |  | 0 |  |
Purchases |  | 0 |  |
Reductions |  | (1,467) |  |
Transfers in/(out) at fair value |  | 4,598 |  |
Discount accretion |  | 3 |  |
Net unrealized appreciation (depreciation) on investments |  | (3,001) |  |
Net realized gain (loss) on investments |  | 0 |  |
Investments, fair value |  | 133 | 0 |
Interest income |  | 163 |  |
Transfers in/(out) at fair value |  | 4,598 |  |
Investments, fair value |  | (133) | 0 |
Investment, Affiliated Issuer, Noncontrolled [Member] | Evelo Biosciences, Inc. [Member] | Investment Five [Member] |  |  |  |
Investments, fair value |  | 0 |  |
Purchases |  | 0 |  |
Reductions |  | (978) |  |
Transfers in/(out) at fair value |  | 3,067 |  |
Discount accretion |  | 4 |  |
Net unrealized appreciation (depreciation) on investments |  | (2,005) |  |
Net realized gain (loss) on investments |  | 0 |  |
Investments, fair value |  | 88 | 0 |
Interest income |  | 114 |  |
Transfers in/(out) at fair value |  | 3,067 |  |
Investments, fair value |  | (88) | 0 |
Investment, Affiliated Issuer, Noncontrolled [Member] | Evelo Biosciences, Inc. [Member] | Investment Six [Member] |  |  |  |
Investments, fair value |  | 0 |  |
Purchases |  | 0 |  |
Reductions |  | (978) |  |
Transfers in/(out) at fair value |  | 3,067 |  |
Discount accretion |  | 4 |  |
Net unrealized appreciation (depreciation) on investments |  | (2,005) |  |
Net realized gain (loss) on investments |  | 0 |  |
Investments, fair value |  | 88 | 0 |
Interest income |  | 111 |  |
Transfers in/(out) at fair value |  | 3,067 |  |
Investments, fair value |  | (88) | 0 |
Investment, Affiliated Issuer, Noncontrolled [Member] | Evelo Biosciences, Inc. [Member] | Investment Seven [Member] |  |  |  |
Investments, fair value |  | 0 |  |
Purchases |  | 0 |  |
Reductions |  | 0 |  |
Transfers in/(out) at fair value |  | 5,000 |  |
Discount accretion |  | 0 |  |
Net unrealized appreciation (depreciation) on investments |  | (4,868) |  |
Net realized gain (loss) on investments |  | 0 |  |
Investments, fair value |  | 132 | 0 |
Interest income |  | 0 |  |
Transfers in/(out) at fair value |  | 5,000 |  |
Investments, fair value |  | (132) | 0 |
Investment, Affiliated Issuer, Controlled [Member] |  |  |  |
Investments, fair value |  | 0 | 0 |
Purchases |  | 1,457 | 0 |
Reductions |  | (516) | (300) |
Transfers in/(out) at fair value |  | 10,734 | 0 |
Discount accretion |  | 6 | 0 |
Net unrealized appreciation (depreciation) on investments |  | 2,222 | 1,450 | (1,450)
Net realized gain (loss) on investments |  | 0 | (1,150) | 0
Investments, fair value |  | 14,223 | 0 | 0
Interest income |  | 17 | 0 | 0
Interest Income, Operating, Paid in Kind |  | 320 | 0 | 0
Transfers in/(out) at fair value |  | 10,734 | 0 |
Investments, fair value |  | (14,223) | 0 | 0
Investment, Affiliated Issuer, Controlled [Member] | Investment [Member] |  |  |  |
Interest income |  | 337 |  |
Investment, Affiliated Issuer, Controlled [Member] | Better Place Forests Co. [Member] | Investment One [Member] |  |  |  |
Investments, fair value |  | 0 |  |
Purchases |  | 61 |  |
Reductions |  | 0 |  |
Transfers in/(out) at fair value |  | 1,675 |  |
Discount accretion |  | 5 |  |
Net unrealized appreciation (depreciation) on investments |  | 1,385 |  |
Net realized gain (loss) on investments |  | 0 |  |
Investments, fair value |  | 3,339 | 0 |
Interest income |  | 225 |  |
Interest Income, Operating, Paid in Kind |  | 213 |  |
Transfers in/(out) at fair value |  | 1,675 |  |
Investments, fair value |  | (3,339) | 0 |
Investment, Affiliated Issuer, Controlled [Member] | Better Place Forests Co. [Member] | Investment Two [Member] |  |  |  |
Investments, fair value |  | 0 |  |
Purchases |  | 0 |  |
Reductions |  | 0 |  |
Transfers in/(out) at fair value |  | 844 |  |
Discount accretion |  | 1 |  |
Net unrealized appreciation (depreciation) on investments |  | 678 |  |
Net realized gain (loss) on investments |  | 0 |  |
Investments, fair value |  | 1,630 | 0 |
Interest income |  | 112 |  |
Interest Income, Operating, Paid in Kind |  | 107 |  |
Transfers in/(out) at fair value |  | 844 |  |
Investments, fair value |  | (1,630) | 0 |
Investment, Affiliated Issuer, Controlled [Member] | Better Place Forests Co. [Member] | Investment Three [Member] |  |  |  |
Investments, fair value |  | 0 |  |
Purchases |  | 1,250 |  |
Reductions |  | 0 |  |
Transfers in/(out) at fair value |  | 2,061 |  |
Discount accretion |  | 0 |  |
Net unrealized appreciation (depreciation) on investments |  | (287) |  |
Net realized gain (loss) on investments |  | 0 |  |
Investments, fair value |  | 3,024 | 0 |
Interest income |  | 0 |  |
Interest Income, Operating, Paid in Kind |  | 0 |  |
Transfers in/(out) at fair value |  | 2,061 |  |
Investments, fair value |  | (3,024) | 0 |
Investment, Affiliated Issuer, Controlled [Member] | HESP LLC [Member] |  |  |  |
Investments, fair value |  | 0 | 0 |
Purchases |  |  | 0 |
Reductions |  |  | (300) |
Transfers in/(out) at fair value |  |  | 0 |
Discount accretion |  |  | 0 |
Net unrealized appreciation (depreciation) on investments |  |  | 1,450 |
Net realized gain (loss) on investments |  |  | (1,150) |
Investments, fair value |  |  | 0 | 0
Interest income |  |  | 0 |
Transfers in/(out) at fair value |  |  | 0 |
Investments, fair value |  |  | 0 | $ 0
Investment, Affiliated Issuer, Controlled [Member] | HIMV LLC [Member] |  |  |  |
Investments, fair value |  | 0 |  |
Purchases |  | 146 |  |
Reductions |  | (516) |  |
Transfers in/(out) at fair value |  | 6,154 |  |
Discount accretion |  | 0 |  |
Net unrealized appreciation (depreciation) on investments |  | 446 |  |
Net realized gain (loss) on investments |  | 0 |  |
Investments, fair value |  | 6,230 | 0 |
Interest income |  | 0 |  |
Interest Income, Operating, Paid in Kind |  | 0 |  |
Transfers in/(out) at fair value |  | 6,154 |  |
Investments, fair value |  | $ (6,230) | $ 0 |
[1] | As of December 31, 2023, the Company no longer owns 5% of more of the portfolio company.

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