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Portfolio Company Investments - Schedule of Consolidated Schedule of Investments in and Advances to Affiliates (Details) - USD ($) $ in Thousands | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2023 | Dec. 31, 2022
Investments in and Advances to Affiliates [Line Items] |  |  |  |  |
Fair Value, beginning balance | [1],[2],[3],[4] | $ 860,329 |  |  |
Fair Value, ending balance |  | 926,859 | [5],[6],[7],[8] | $ 860,329 | [1],[2],[3],[4]
Control Investments |  |  |  |  |
Investments in and Advances to Affiliates [Line Items] |  |  |  |  |
Principal Amount - Debt Investments |  | 5,226 |  | 14,576 |
Fair Value, beginning balance |  |  |  | 2,151 |
Gross Additions |  | 11,458 |  | 20,174 |
Gross Reductions |  | (11,458) |  | (22,325) |
Net Realized Gain (Losses) |  | (11,458) |  | (158) |
Net Change in Unrealized Appreciation (Depreciation) |  | 11,083 |  | (13,233) |
Affiliate Investments |  |  |  |  |
Investments in and Advances to Affiliates [Line Items] |  |  |  |  |
Principal Amount - Debt Investments |  | 24,602 |  | 34,602 |
Fair Value, beginning balance |  | 101,590 |  | 137,284 |
Gross Additions |  | 5,118 |  | 70,477 |
Gross Reductions |  | (23,551) |  | (106,171) |
Fair Value, ending balance |  | 83,157 |  | 101,590 |
Net Realized Gain (Losses) |  |  |  | 39,833 |
Net Change in Unrealized Appreciation (Depreciation) |  | (9,109) |  | (35,979) |
Interest Income |  | 3,168 |  | 3,464 |
Payment-in-kind Interest Income |  |  |  | 30 |
Dividend Income |  | 519 |  | 725 |
Fee Income |  | 60 |  | 457 |
EBL, LLC (EbLens) | Control Investments |  |  |  |  |
Investments in and Advances to Affiliates [Line Items] |  |  |  |  |
Principal Amount - Debt Investments |  |  |  | 9,350 |
Gross Additions |  | 11,458 |  | 19,628 |
Gross Reductions |  | (11,458) |  | (19,628) |
Net Realized Gain (Losses) |  | (11,458) |  |  |
Net Change in Unrealized Appreciation (Depreciation) |  | 11,083 |  | (11,083) |
Hilco Plastics Holdings, LLC (dba Hilco Technologies) | Control Investments |  |  |  |  |
Investments in and Advances to Affiliates [Line Items] |  |  |  |  |
Gross Additions |  |  |  | 353 |
Gross Reductions |  |  |  | (353) |
Net Realized Gain (Losses) |  |  |  | (352) |
Mesa Line Services, LLC | Control Investments |  |  |  |  |
Investments in and Advances to Affiliates [Line Items] |  |  |  |  |
Fair Value, beginning balance |  |  |  | 2,151 |
Gross Additions |  |  |  | 193 |
Gross Reductions |  |  |  | (2,344) |
Net Realized Gain (Losses) |  |  |  | 194 |
Net Change in Unrealized Appreciation (Depreciation) |  |  |  | (2,150) |
US GreenFiber, LLC | Control Investments |  |  |  |  |
Investments in and Advances to Affiliates [Line Items] |  |  |  |  |
Principal Amount - Debt Investments |  | 5,226 |  | 5,226 |
Applegate Greenfiber Intermediate Inc. (fka US GreenFiber, LLC) | Affiliate Investments |  |  |  |  |
Investments in and Advances to Affiliates [Line Items] |  |  |  |  |
Principal Amount - Debt Investments |  | 9,602 |  | 9,602 |
Fair Value, beginning balance |  | 23,168 |  | 22,405 |
Gross Additions |  | 642 |  | 13,566 |
Gross Reductions |  |  |  | (12,803) |
Fair Value, ending balance |  | 23,810 |  | 23,168 |
Net Change in Unrealized Appreciation (Depreciation) |  | 643 |  | 763 |
Interest Income |  | 728 |  | 973 |
FAR Research Inc. | Affiliate Investments |  |  |  |  |
Investments in and Advances to Affiliates [Line Items] |  |  |  |  |
Fair Value, beginning balance |  |  |  | 28 |
Gross Reductions |  |  |  | (28) |
Net Change in Unrealized Appreciation (Depreciation) |  |  |  | (28) |
Medsurant Holdings, LLC | Affiliate Investments |  |  |  |  |
Investments in and Advances to Affiliates [Line Items] |  |  |  |  |
Fair Value, beginning balance |  | 2,540 |  | 3,662 |
Gross Additions |  | 2,130 |  |  |
Gross Reductions |  | (73) |  | (1,122) |
Fair Value, ending balance |  | 4,597 |  | 2,540 |
Net Change in Unrealized Appreciation (Depreciation) |  | 2,130 |  | (1,122) |
Mirage Trailers LLC | Affiliate Investments |  |  |  |  |
Investments in and Advances to Affiliates [Line Items] |  |  |  |  |
Fair Value, beginning balance |  |  |  | 10,675 |
Gross Additions |  |  |  | 355 |
Gross Reductions |  |  |  | (11,030) |
Net Realized Gain (Losses) |  |  |  | 324 |
Net Change in Unrealized Appreciation (Depreciation) |  |  |  | (1,694) |
Interest Income |  |  |  | 248 |
Payment-in-kind Interest Income |  |  |  | 29 |
Fee Income |  |  |  | 132 |
Pfanstiehl, Inc | Affiliate Investments |  |  |  |  |
Investments in and Advances to Affiliates [Line Items] |  |  |  |  |
Principal Amount - Debt Investments |  |  |  | 10,000 |
Fair Value, beginning balance |  | 51,992 |  | 57,639 |
Gross Additions |  | 46 |  | 34,335 |
Gross Reductions |  | (18,268) |  | (39,982) |
Fair Value, ending balance |  | 33,770 |  | 51,992 |
Net Realized Gain (Losses) |  |  |  | 24,330 |
Net Change in Unrealized Appreciation (Depreciation) |  | (8,268) |  | (15,432) |
Interest Income |  | 673 |  | 421 |
Dividend Income |  | 347 |  |  |
Fee Income |  |  |  | 150 |
Pinnergy, Ltd. | Affiliate Investments |  |  |  |  |
Investments in and Advances to Affiliates [Line Items] |  |  |  |  |
Fair Value, beginning balance |  |  |  | 21,178 |
Gross Additions |  |  |  | 15,300 |
Gross Reductions |  |  |  | (36,478) |
Net Realized Gain (Losses) |  |  |  | 15,300 |
Net Change in Unrealized Appreciation (Depreciation) |  |  |  | (18,177) |
Dividend Income |  |  |  | 656 |
Spectra A&D Acquisition, Inc. (fka FDS Avionics Corp.) | Affiliate Investments |  |  |  |  |
Investments in and Advances to Affiliates [Line Items] |  |  |  |  |
Principal Amount - Debt Investments |  | 15,000 |  | 15,000 |
Fair Value, beginning balance |  | 19,118 |  | 18,359 |
Gross Additions |  | 2,203 |  | 5,487 |
Gross Reductions |  | (5,210) |  | (4,728) |
Fair Value, ending balance |  | 16,111 |  | 19,118 |
Net Realized Gain (Losses) |  |  |  | (121) |
Net Change in Unrealized Appreciation (Depreciation) |  | (3,711) |  | (1,723) |
Interest Income |  | 1,767 |  | 1,822 |
Fee Income |  | 60 |  | 175 |
Steward Holding LLC (dba Steward Advanced Materials) | Affiliate Investments |  |  |  |  |
Investments in and Advances to Affiliates [Line Items] |  |  |  |  |
Fair Value, beginning balance |  | 4,772 |  | 3,338 |
Gross Additions |  | 97 |  | 1,434 |
Fair Value, ending balance |  | 4,869 |  | 4,772 |
Net Change in Unrealized Appreciation (Depreciation) |  | 97 |  | 1,434 |
Payment-in-kind Interest Income |  |  |  | 1 |
Dividend Income |  | $ 172 |  | $ 69 |
[1] | (a) See Note 3 to the consolidated financial statements for portfolio composition by geographic location.
[2] | (b) Equity ownership may be held in shares or units of companies related to the portfolio companies.
[3] | (c) All debt investments are income producing, unless otherwise indicated. Equity investments are non-income producing unless otherwise noted.
[4] | (g) Except as otherwise noted, the Company’s investment portfolio is comprised of debt and equity securities of privately held companies for which quoted prices falling within the categories of Level 1 and Level 2 inputs are not available. Therefore, the Company values all of its portfolio investments at fair value, as determined in good faith by the board of directors, using significant unobservable Level 3 inputs.
[5] | (a) See Note 3 to the consolidated financial statements for portfolio composition by geographic location.
[6] | (b) Equity ownership may be held in shares or units of companies related to the portfolio companies.
[7] | (c) All debt investments are income producing, unless otherwise indicated. Equity investments are non-income producing unless otherwise noted.
[8] | (g) Except as otherwise noted, the Company’s investment portfolio is comprised of debt and equity securities of privately held companies for which quoted prices falling within the categories of Level 1 and Level 2 inputs are not available. Therefore, the Company values all of its portfolio investments at fair value, as determined in good faith by the board of directors, using significant unobservable Level 3 inputs.

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