| INVESTMENTS IN AND ADVANCES TO AFFILIATES (Details) - USD ($)
 | 12 Months Ended | 
| Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2021 | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 172.50% | [1],[2],[3],[4],[5] | 205.90% | [6],[7],[8],[9],[10] |  | 
| Net Realized Gain (Loss) for Period |  | $ 12,664,000 |  | $ 5,173,000 |  | $ 3,180,000 | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [9] | 649,615,000 |  |  |  |  | 
| Ending Balance |  | 704,815,000 | [4] | 649,615,000 | [9] |  | 
| Diversified/Conglomerate Manufacturing |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 114,105,000 |  |  |  |  | 
| Ending Balance |  | 158,061,000 |  | 114,105,000 |  |  | 
| Diversified/Conglomerate Service |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 148,907,000 |  |  |  |  | 
| Ending Balance |  | 135,060,000 |  | 148,907,000 |  |  | 
| Automobile |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 20,144,000 |  |  |  |  | 
| Ending Balance |  | 27,571,000 |  | 20,144,000 |  |  | 
| Machinery |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 9,562,000 |  |  |  |  | 
| Ending Balance |  | 6,411,000 |  | 9,562,000 |  |  | 
| Secured first lien debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 463,858,000 |  |  |  |  | 
| Ending Balance |  | 510,701,000 |  | 463,858,000 |  |  | 
| Secured second lien debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 115,928,000 |  |  |  |  | 
| Ending Balance |  | 127,854,000 |  | 115,928,000 |  |  | 
| Unsecured debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 55,000 |  |  |  |  | 
| Ending Balance |  | 24,000 |  | 55,000 |  |  | 
| Preferred equity |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 27,046,000 |  |  |  |  | 
| Ending Balance |  | 26,855,000 |  | 27,046,000 |  |  | 
| Common equity/equivalents |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 42,728,000 |  |  |  |  | 
| Ending Balance |  | $ 39,381,000 |  | $ 42,728,000 |  |  | 
| Affiliate investments |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 2.60% | [1],[2],[3],[5],[11] | 12.40% | [6],[7],[8],[10],[12] |  | 
| Net Realized Gain (Loss) for Period |  | $ 0 |  | $ 13,408,000 |  | 0 | 
| Amount of Investment Income |  | 4,753,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [12] | 39,091,000 |  |  |  |  | 
| Gross Additions |  | 1,056,000 |  |  |  |  | 
| Gross Reductions |  | (33,722,000) |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 3,996,000 |  |  |  |  | 
| Ending Balance |  | $ 10,421,000 | [11] | $ 39,091,000 | [12] |  | 
| Affiliate investments | Secured first lien debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 0.70% | [1],[2],[3],[5],[11] | 11.00% | [6],[7],[8],[10],[12] |  | 
| Net Realized Gain (Loss) for Period |  | $ 0 |  |  |  |  | 
| Amount of Investment Income |  | 4,753,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [12] | 34,804,000 |  |  |  |  | 
| Gross Additions |  | 556,000 |  |  |  |  | 
| Gross Reductions |  | (33,722,000) |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 1,257,000 |  |  |  |  | 
| Ending Balance |  | $ 2,895,000 |  | $ 34,804,000 | [12] |  | 
| Affiliate investments | Secured first lien debt | Diversified/Conglomerate Manufacturing |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 0.70% |  | 0.80% | [6],[7],[8],[10],[12] |  | 
| Affiliate investments | Secured first lien debt | Diversified/Conglomerate Service |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 0.00% |  | 10.20% | [6],[7],[8],[10],[12] |  | 
| Net Realized Gain (Loss) for Period |  | $ 0 |  |  |  |  | 
| Amount of Investment Income |  | 4,795,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [12] | 32,254,000 |  |  |  |  | 
| Gross Additions |  | 556,000 |  |  |  |  | 
| Gross Reductions |  | (33,722,000) |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 912,000 |  |  |  |  | 
| Ending Balance |  | $ 0 |  | $ 32,254,000 | [12] |  | 
| Affiliate investments | Preferred equity |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 1.30% | [1],[2],[3],[5],[11] | 1.20% | [6],[7],[8],[10],[12] |  | 
| Net Realized Gain (Loss) for Period |  | $ 0 |  |  |  |  | 
| Amount of Investment Income |  | 0 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [12] | 3,640,000 |  |  |  |  | 
| Gross Additions |  | 0 |  |  |  |  | 
| Gross Reductions |  | 0 |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 1,482,000 |  |  |  |  | 
| Ending Balance |  | $ 5,122,000 | [11] | $ 3,640,000 | [12] |  | 
| Affiliate investments | Preferred equity | Diversified/Conglomerate Manufacturing |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 0.00% | [1],[2],[3],[5],[11] | 0.00% | [6],[7],[8],[10],[12] |  | 
| Affiliate investments | Preferred equity | Diversified/Conglomerate Service |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 1.10% | [1],[2],[3],[5],[11] | 0.90% | [6],[7],[8],[10],[12] |  | 
| Affiliate investments | Preferred equity | Personal and Non-Durable Consumer Products (Manufacturing Only) |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 0.20% | [1],[2],[3],[5],[11] | 0.30% | [6],[7],[8],[10],[12] |  | 
| Affiliate investments | Common equity/equivalents |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 0.60% | [1],[2],[3],[5],[11] | 0.20% | [6],[7],[8],[10],[12] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [12] | $ 647,000 |  |  |  |  | 
| Ending Balance | [12] |  |  | $ 647,000 |  |  | 
| Affiliate investments | Common equity/equivalents | Personal and Non-Durable Consumer Products (Manufacturing Only) |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 0.60% |  | 0.20% | [6],[7],[8],[10],[12] |  | 
| Control investments |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 7.50% | [1],[2],[3],[5],[13] | 11.30% | [6],[7],[8],[10],[14] |  | 
| Net Realized Gain (Loss) for Period |  | $ 2,684,000 |  | $ (8,496,000) |  | $ 0 | 
| Amount of Investment Income |  | 3,883,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [14] | 35,713,000 |  |  |  |  | 
| Gross Additions |  | 677,000 |  |  |  |  | 
| Gross Reductions |  | (1,456,000) |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | (4,084,000) |  |  |  |  | 
| Ending Balance |  | $ 30,850,000 | [13] | $ 35,713,000 | [14] |  | 
| Control investments | Secured first lien debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 3.90% | [1],[2],[3],[5],[13] | 4.90% | [6],[7],[8],[10],[14] |  | 
| Net Realized Gain (Loss) for Period |  | $ 0 |  |  |  |  | 
| Amount of Investment Income |  | 2,117,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 15,423,000 |  |  |  |  | 
| Gross Additions |  | 677,000 |  |  |  |  | 
| Gross Reductions |  | (200,000) |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 220,000 |  |  |  |  | 
| Ending Balance |  | $ 16,120,000 | [13] | $ 15,423,000 |  |  | 
| Control investments | Secured first lien debt | Diversified/Conglomerate Manufacturing |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 0.90% | [1],[2],[3],[5],[13] | 1.00% | [6],[7],[8],[10],[14] |  | 
| Control investments | Secured first lien debt | Personal and Non-Durable Consumer Products (Manufacturing Only) |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 2.80% | [1],[2],[3],[5],[13] | 3.60% | [6],[7],[8],[10],[14] |  | 
| Net Realized Gain (Loss) for Period |  | $ 0 |  |  |  |  | 
| Amount of Investment Income |  | 1,740,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [14] | 11,393,000 |  |  |  |  | 
| Gross Additions |  | 0 |  |  |  |  | 
| Gross Reductions |  | (100,000) |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 0 |  |  |  |  | 
| Ending Balance |  | $ 11,293,000 | [13] | $ 11,393,000 | [14] |  | 
| Control investments | Secured first lien debt | Printing and Publishing |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 0.20% | [1],[2],[3],[5],[13] | 0.30% | [6],[7],[8],[10],[14] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [14] | $ 15,423,000 |  |  |  |  | 
| Ending Balance | [14] |  |  | $ 15,423,000 |  |  | 
| Control investments | Secured second lien debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 1.80% | [1],[2],[3],[5],[13] | 2.40% | [6],[7],[8],[10],[14] |  | 
| Control investments | Secured second lien debt | Automobile |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 1.80% |  | 2.40% | [6],[7],[8],[10],[14] |  | 
| Control investments | Unsecured debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 0.00% |  | 0.00% | [6],[7],[8],[10],[14] |  | 
| Control investments | Unsecured debt | Diversified/Conglomerate Manufacturing |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 0.00% |  | 0.00% | [6],[7],[8],[10],[14] |  | 
| Control investments | Preferred equity |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 0.00% | [1],[2],[3],[5],[13] | 1.80% | [6],[7],[8],[10],[14] |  | 
| Control investments | Preferred equity | Personal and Non-Durable Consumer Products (Manufacturing Only) |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 0.00% |  | 1.80% | [6],[7],[8],[10],[14] |  | 
| Control investments | Common equity/equivalents |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 1.80% | [1],[2],[3],[5],[13] | 2.20% | [6],[7],[8],[10],[14] |  | 
| Net Realized Gain (Loss) for Period |  | $ 2,779,000 |  |  |  |  | 
| Amount of Investment Income |  | 691,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [14] | 6,938,000 |  |  |  |  | 
| Gross Additions |  | 0 |  |  |  |  | 
| Gross Reductions |  | (921,000) |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 1,288,000 |  |  |  |  | 
| Ending Balance |  | $ 7,305,000 | [13] | $ 6,938,000 | [14] |  | 
| Control investments | Common equity/equivalents | Diversified/Conglomerate Manufacturing |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 0.00% | [1],[2],[3],[5],[13] | 0.00% | [6],[7],[8],[10],[14] |  | 
| Net Realized Gain (Loss) for Period |  | $ (921,000) |  |  |  |  | 
| Amount of Investment Income |  | 0 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [14] | 0 |  |  |  |  | 
| Gross Additions |  | 0 |  |  |  |  | 
| Gross Reductions |  | (921,000) |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 921,000 |  |  |  |  | 
| Ending Balance |  | $ 0 |  | $ 0 | [14] |  | 
| Control investments | Common equity/equivalents | Printing and Publishing |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 0.70% | [1],[2],[3],[5],[13] | 0.70% |  |  | 
| Control investments | Common equity/equivalents | Automobile |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 1.00% | [1],[2],[3],[5],[13] | 0.40% | [6],[7],[8],[10],[14] |  | 
| Control investments | Common equity/equivalents | Machinery |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Investment owned, percent of net assets |  | 0.10% | [1],[2],[3],[5],[13] | 1.10% | [6],[7],[8],[10],[14] |  | 
| Investment, Identifier [Axis]: Leeds Novamark Capital I, L.P. – Limited Partnership Interest |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Units | [15],[16],[17],[18],[19] |  |  | 3.50% |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [16],[18],[19] | $ 6,397,000 |  |  |  |  | 
| Ending Balance | [16],[18],[19] |  |  | $ 6,397,000 |  |  | 
| Line of credit facility, available | [6],[7],[8],[10],[16],[18],[19] |  |  | $ 843,000 |  |  | 
| Investment, Identifier [Axis]: Antenna Research Associates, Inc. – Common Equity Units |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares | [15],[17],[18],[20] |  |  | 4,283 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | 13,734,000 |  |  |  |  | 
| Ending Balance | [18],[20] |  |  | $ 13,734,000 |  |  | 
| Investment, Identifier [Axis]: Engineering Manufacturing Technologies, LLC – Common Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares | [15],[17],[18],[20] |  |  | 6,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | 1,773,000 |  |  |  |  | 
| Ending Balance | [18],[20] |  |  | $ 1,773,000 |  |  | 
| Investment, Identifier [Axis]: Ohio Armor Holdings, LLC – Common Equity |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares | [15],[17],[18],[20] |  |  | 100 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | 1,017,000 |  |  |  |  | 
| Ending Balance | [18],[20] |  |  | $ 1,017,000 |  |  | 
| Investment, Identifier [Axis]: 8th Avenue Food & Provisions, Inc. – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 3,683,000 | [21],[22],[23] | 3,682,000 | [15],[17],[24] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [24] | 3,020,000 |  |  |  |  | 
| Ending Balance |  | $ 2,495,000 | [21] | $ 3,020,000 | [24] |  | 
| Investment, reference rate and spread |  | 7.90% | [1],[2],[3],[5],[21] | 7.80% | [6],[7],[8],[10],[24] |  | 
| Investment, interest rate, paid in cash |  | 13.20% | [1],[2],[3],[5],[21] | 10.90% | [6],[7],[8],[10],[24] |  | 
| Investment, Identifier [Axis]: ALS Education, LLC – Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | $ 0 | [22],[23],[25] | $ 0 | [15],[17],[26] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | 0 |  |  |  |  | 
| Ending Balance |  | 0 | [25] | 0 | [26] |  | 
| Line of credit facility, available |  | $ 3,000,000 | [1],[2],[3],[5],[25] | $ 3,000,000 | [6],[7],[8],[10],[26] |  | 
| Investment, reference rate and spread |  | 7.00% | [1],[2],[3],[5],[25] | 7.00% | [6],[7],[8],[10],[26] |  | 
| Investment, interest rate, paid in cash |  | 12.30% | [1],[2],[3],[5],[25] | 10.10% | [6],[7],[8],[10],[26] |  | 
| Investment, Identifier [Axis]: ALS Education, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | $ 18,700,000 | [22],[23],[25] | $ 19,690,000 | [15],[17],[26] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | 19,468,000 |  |  |  |  | 
| Ending Balance |  | $ 18,700,000 | [25] | $ 19,468,000 | [26] |  | 
| Investment, reference rate and spread |  | 7.00% | [1],[2],[3],[5],[25] | 7.00% | [6],[7],[8],[10],[26] |  | 
| Investment, interest rate, paid in cash |  | 12.30% | [1],[2],[3],[5],[25] | 10.10% | [6],[7],[8],[10],[26] |  | 
| Investment, Identifier [Axis]: Antenna Research Associates, Inc. – Common Equity Units |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares | [22],[23],[27],[28] | 4,283,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [27],[28] | $ 18,436,000 |  |  |  |  | 
| Investment, Identifier [Axis]: Antenna Research Associates, Inc. – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 30,048,000 | [22],[23],[27] | $ 21,973,000 | [15],[17],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [20] | 21,973,000 |  |  |  |  | 
| Ending Balance |  | $ 30,048,000 | [27] | $ 21,973,000 | [20] |  | 
| Investment, interest rate, paid in kind |  | 4.00% | [1],[2],[3],[5],[27] | 4.00% | [6],[7],[8],[10],[20] |  | 
| Investment, reference rate and spread |  | 10.00% | [1],[2],[3],[5],[27] | 10.00% | [6],[7],[8],[10],[20] |  | 
| Investment, interest rate, paid in cash |  | 15.30% | [1],[2],[3],[5],[27] | 13.00% | [6],[7],[8],[10],[20] |  | 
| Investment, Identifier [Axis]: Arc Drilling Holdings LLC – Common Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 15,000,000 | [22],[23],[27],[28] | 15,000 | [15],[17],[18],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 0 |  |  |  |  | 
| Ending Balance |  | 403,000 | [27],[28] | $ 0 | [18],[20] |  | 
| Investment, Identifier [Axis]: Arc Drilling Holdings LLC – Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 0 | [22],[23],[25] | 0 | [15],[17],[26] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | 0 |  |  |  |  | 
| Ending Balance |  | $ 0 | [25] | 0 | [26] |  | 
| Investment, interest rate, paid in kind | [1],[2],[3],[5],[25] | 6.30% |  |  |  |  | 
| Line of credit facility, available |  | $ 1,000,000 | [1],[2],[3],[5],[25] | $ 1,000,000 | [6],[7],[8],[10],[26] |  | 
| Investment, reference rate and spread |  | 11.50% | [1],[2],[3],[5],[25] | 8.00% | [6],[7],[8],[10],[26] |  | 
| Investment, interest rate, paid in cash |  | 10.50% | [1],[2],[3],[5],[25] | 11.10% | [6],[7],[8],[10],[26] |  | 
| Investment, Identifier [Axis]: Arc Drilling Holdings LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25] | $ 5,928,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25] | $ 5,724,000 |  |  |  |  | 
| Investment, interest rate, paid in kind | [1],[2],[3],[5],[25] | 6.30% |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[25] | 11.50% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25] | 10.50% |  |  |  |  | 
| Investment, Identifier [Axis]: Arc Drilling Holdings LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[26] |  |  | $ 5,625,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | $ 5,350,000 |  |  |  |  | 
| Ending Balance | [26] |  |  | $ 5,350,000 |  |  | 
| Investment, interest rate, paid in kind | [6],[7],[8],[10],[26] |  |  | 3.00% |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[26] |  |  | 9.50% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[26] |  |  | 12.60% |  |  | 
| Investment, Identifier [Axis]: Axios Industrial Group, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 11,550,000 | [22],[23],[25] | $ 9,000,000 | [15],[17],[26],[29] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26],[29] | 8,741,000 |  |  |  |  | 
| Ending Balance |  | $ 11,291,000 | [25] | $ 8,741,000 | [26],[29] |  | 
| Investment, reference rate and spread |  | 8.60% | [1],[2],[3],[5],[25] | 9.50% | [6],[7],[8],[10],[26],[29] |  | 
| Investment, interest rate, paid in cash |  | 13.90% | [1],[2],[3],[5],[25] | 12.60% | [6],[7],[8],[10],[26],[29] |  | 
| Investment, Identifier [Axis]: Axios Industrial Group, LLC– Delayed Draw Term Loan |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[26],[29] |  |  | $ 3,000,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26],[29] | $ 2,914,000 |  |  |  |  | 
| Ending Balance | [26],[29] |  |  | 2,914,000 |  |  | 
| Line of credit facility, available | [6],[7],[8],[10],[26],[29] |  |  | $ 5,000,000 |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[26],[29] |  |  | 9.50% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[26],[29] |  |  | 12.60% |  |  | 
| Investment, Identifier [Axis]: B+T Group Acquisition, Inc. – Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25],[30] | 1,200,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25],[30] | 978,000 |  |  |  |  | 
| Line of credit facility, available | [1],[2],[3],[5],[25],[30] | $ 0 |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[25],[30] | 2.00% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25],[30] | 7.30% |  |  |  |  | 
| Investment, Identifier [Axis]: B+T Group Acquisition, Inc. – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25],[30] | $ 6,000,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25],[30] | $ 4,890,000 |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[25],[30] | 2.00% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25],[30] | 7.30% |  |  |  |  | 
| Investment, Identifier [Axis]: B+T Group Acquisition, Inc.(S) – Common Stock Warrant |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Units |  | 1.50% | [22],[23],[27],[28],[30] | 1.50% | [15],[17],[18],[20],[31] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20],[31] | $ 25,000 |  |  |  |  | 
| Ending Balance |  | 0 | [27],[28],[30] | $ 25,000 | [18],[20],[31] |  | 
| Investment, Identifier [Axis]: B+T Group Acquisition, Inc.(S) – Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[26],[31] |  |  | 1,200,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26],[31] | $ 1,146,000 |  |  |  |  | 
| Ending Balance | [26],[31] |  |  | 1,146,000 |  |  | 
| Line of credit facility, available | [6],[7],[8],[10],[26],[31] |  |  | $ 0 |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[26],[31] |  |  | 11.00% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[26],[31] |  |  | 14.10% |  |  | 
| Investment, Identifier [Axis]: B+T Group Acquisition, Inc.(S) – Preferred Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 6,130,000 | [22],[23],[27],[28],[30] | 6,130 | [15],[17],[18],[20],[31] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20],[31] | $ 2,718,000 |  |  |  |  | 
| Ending Balance |  | 0 | [27],[28],[30] | $ 2,718,000 | [18],[20],[31] |  | 
| Investment, Identifier [Axis]: B+T Group Acquisition, Inc.(S) – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[26],[31] |  |  | 6,000,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26],[31] | 5,730,000 |  |  |  |  | 
| Ending Balance | [26],[31] |  |  | $ 5,730,000 |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[26],[31] |  |  | 11.00% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[26],[31] |  |  | 14.10% |  |  | 
| Investment, Identifier [Axis]: CHA Holdings, Inc. – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [21],[22],[23],[32] | 3,000,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [21],[32] | $ 2,820,000 |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[21],[32] | 9.00% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[21],[32] | 14.40% |  |  |  |  | 
| Investment, Identifier [Axis]: CHA Holdings, Inc. – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[24],[33] |  |  | $ 3,000,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [24],[33] | $ 2,700,000 |  |  |  |  | 
| Ending Balance | [24],[33] |  |  | $ 2,700,000 |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[24],[33] |  |  | 8.80% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[24],[33] |  |  | 12.50% |  |  | 
| Investment, Identifier [Axis]: CPM Holdings, Inc. – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[24] |  |  | $ 798,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [24] | 758,000 |  |  |  |  | 
| Ending Balance | [24] |  |  | $ 758,000 |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[24] |  |  | 8.30% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[24] |  |  | 11.40% |  |  | 
| Investment, Identifier [Axis]: Cafe Zupas – Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25] | 0 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25] | 0 |  |  |  |  | 
| Line of credit facility, available | [1],[2],[3],[5],[25] | $ 1,500,000 |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[25] | 6.80% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25] | 12.10% |  |  |  |  | 
| Investment, Identifier [Axis]: Café Zupas – Delayed Draw Term Loan |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | $ 7,970,000 | [22],[23],[25] | $ 1,970,000 | [15],[17],[26] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | 1,958,000 |  |  |  |  | 
| Ending Balance |  | 7,850,000 | [25] | 1,958,000 | [26] |  | 
| Line of credit facility, available |  | $ 2,070,000 | [1],[2],[3],[5],[25] | $ 0 | [6],[7],[8],[10],[26] |  | 
| Investment, reference rate and spread |  | 6.80% | [1],[2],[3],[5],[25] | 7.40% | [6],[7],[8],[10],[26] |  | 
| Investment, interest rate, paid in cash |  | 12.10% | [1],[2],[3],[5],[25] | 10.50% | [6],[7],[8],[10],[26] |  | 
| Investment, Identifier [Axis]: Café Zupas – Line of Credit, |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[26] |  |  | $ 0 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | $ 0 |  |  |  |  | 
| Ending Balance | [26] |  |  | 0 |  |  | 
| Line of credit facility, available | [6],[7],[8],[10],[26] |  |  | $ 4,000,000 |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[26] |  |  | 7.40% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[26] |  |  | 10.50% |  |  | 
| Investment, Identifier [Axis]: Café Zupas – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 23,460,000 | [22],[23],[25] | $ 23,460,000 | [15],[17],[26] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | 23,313,000 |  |  |  |  | 
| Ending Balance |  | $ 23,108,000 | [25] | $ 23,313,000 | [26] |  | 
| Investment, reference rate and spread |  | 6.80% | [1],[2],[3],[5],[25] | 7.40% | [6],[7],[8],[10],[26] |  | 
| Investment, interest rate, paid in cash |  | 12.10% | [1],[2],[3],[5],[25] | 10.50% | [6],[7],[8],[10],[26] |  | 
| Investment, Identifier [Axis]: Canopy Safety Brands, LLC – Common Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 1,170,370,000 | [22],[23],[27],[28] | 800,000 | [15],[17],[18],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 647,000 |  |  |  |  | 
| Ending Balance |  | $ 2,404,000 | [27],[28] | $ 647,000 | [18],[20] |  | 
| Investment, Identifier [Axis]: Canopy Safety Brands, LLC – Preferred Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 500,000,000 | [22],[23],[27],[28] | 500,000 | [15],[17],[18],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 798,000 |  |  |  |  | 
| Ending Balance |  | $ 857,000 | [27],[28] | $ 798,000 | [18],[20] |  | 
| Investment, Identifier [Axis]: Canopy Safety Brands, LLC—Common Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 1,170,370 |  |  |  |  | 
| Net Realized Gain (Loss) for Period |  | $ 0 |  |  |  |  | 
| Amount of Investment Income |  | 0 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 647,000 |  |  |  |  | 
| Gross Additions |  | 500,000 |  |  |  |  | 
| Gross Reductions |  | 0 |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 1,257,000 |  |  |  |  | 
| Ending Balance |  | $ 2,404,000 |  | 647,000 |  |  | 
| Investment, Identifier [Axis]: Canopy Safety Brands, LLC—Preferred Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 500,000 |  |  |  |  | 
| Net Realized Gain (Loss) for Period |  | $ 0 |  |  |  |  | 
| Amount of Investment Income |  | 0 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 798,000 |  |  |  |  | 
| Gross Additions |  | 0 |  |  |  |  | 
| Gross Reductions |  | 0 |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 59,000 |  |  |  |  | 
| Ending Balance |  | 857,000 |  | 798,000 |  |  | 
| Investment, Identifier [Axis]: Chinese Yellow Pages Company – Line of Credit, |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[20],[34],[35] |  |  | 107,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [20],[34],[35] | 0 |  |  |  |  | 
| Ending Balance | [20],[34],[35] |  |  | 0 |  |  | 
| Line of credit facility, available | [6],[7],[8],[10],[20],[34],[35] |  |  | $ 0 |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[20],[34],[35] |  |  | 4.00% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[20],[34],[35] |  |  | 10.30% |  |  | 
| Investment, Identifier [Axis]: Circuitronics EMS Holdings LLC – Common Units |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares | [15],[17],[18],[20] |  |  | 921,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 0 |  |  |  |  | 
| Ending Balance | [18],[20] |  |  | $ 0 |  |  | 
| Investment, Identifier [Axis]: Circuitronics EMS Holdings LLC—Common Units |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 0 |  |  |  |  | 
| Net Realized Gain (Loss) for Period |  | $ (921,000) |  |  |  |  | 
| Amount of Investment Income |  | 0 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 0 |  |  |  |  | 
| Gross Additions |  | 0 |  |  |  |  | 
| Gross Reductions |  | (921,000) |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 921,000 |  |  |  |  | 
| Ending Balance |  | 0 |  | 0 |  |  | 
| Investment, Identifier [Axis]: DKI Ventures, LLC – Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25],[36] | 205,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25],[36] | 113,000 |  |  |  |  | 
| Line of credit facility, available | [1],[2],[3],[5],[25],[36] | $ 170,000 |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25],[36] | 9.00% |  |  |  |  | 
| Investment, Identifier [Axis]: DKI Ventures, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | $ 5,915,000 | [22],[23],[25],[36] | 5,915,000 | [15],[17],[26] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | 4,554,000 |  |  |  |  | 
| Ending Balance |  | $ 3,253,000 | [25],[36] | $ 4,554,000 | [26] |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[26] |  |  | 8.00% |  |  | 
| Investment, interest rate, paid in cash |  | 9.00% | [1],[2],[3],[5],[25],[36] | 11.00% | [6],[7],[8],[10],[26] |  | 
| Investment, Identifier [Axis]: Defiance Integrated Technologies, Inc. – Common Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 33,321,000 | [22],[23],[27],[28] | 33,321 | [15],[17],[18],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 1,147,000 |  |  |  |  | 
| Ending Balance |  | 3,948,000 | [27],[28] | $ 1,147,000 | [18],[20] |  | 
| Investment, Identifier [Axis]: Defiance Integrated Technologies, Inc. – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[27] | 7,425,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [27] | $ 7,425,000 |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[27] | 9.60% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[27] | 14.90% |  |  |  |  | 
| Investment, Identifier [Axis]: Defiance Integrated Technologies, Inc. – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[20] |  |  | 7,665,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [20] | $ 7,665,000 |  |  |  |  | 
| Ending Balance | [20] |  |  | $ 7,665,000 |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[20] |  |  | 9.50% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[20] |  |  | 12.60% |  |  | 
| Investment, Identifier [Axis]: Defiance Integrated Technologies, Inc.—Common Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 33,321 |  |  |  |  | 
| Net Realized Gain (Loss) for Period |  | $ 0 |  |  |  |  | 
| Amount of Investment Income |  | 0 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 1,147,000 |  |  |  |  | 
| Gross Additions |  | 0 |  |  |  |  | 
| Gross Reductions |  | 0 |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 2,801,000 |  |  |  |  | 
| Ending Balance |  | 3,948,000 |  | $ 1,147,000 |  |  | 
| Investment, Identifier [Axis]: Defiance Integrated Technologies, Inc.—Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 7,425,000 |  |  |  |  | 
| Net Realized Gain (Loss) for Period |  | 0 |  |  |  |  | 
| Amount of Investment Income |  | 1,075,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 7,665,000 |  |  |  |  | 
| Gross Additions |  | 0 |  |  |  |  | 
| Gross Reductions |  | (240,000) |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 0 |  |  |  |  | 
| Ending Balance |  | 7,425,000 |  | 7,665,000 |  |  | 
| Investment, Identifier [Axis]: ENET Holdings, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 22,289,000 | [22],[23],[25] | 24,360,000 | [15],[17],[26] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | 23,142,000 |  |  |  |  | 
| Ending Balance |  | $ 21,397,000 | [25] | $ 23,142,000 | [26] |  | 
| Investment, reference rate and spread |  | 8.30% | [1],[2],[3],[5],[25] | 7.30% | [6],[7],[8],[10],[26] |  | 
| Investment, interest rate, paid in cash |  | 13.60% | [1],[2],[3],[5],[25] | 10.40% | [6],[7],[8],[10],[26] |  | 
| Investment, Identifier [Axis]: Edge Adhesives Holdings, Inc. – Preferred Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 5,466,000 | [22],[23],[27],[28],[30] | 5,466 | [15],[17],[18],[20],[31] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20],[31] | $ 0 |  |  |  |  | 
| Ending Balance |  | 0 | [27],[28],[30] | $ 0 | [18],[20],[31] |  | 
| Investment, Identifier [Axis]: Edge Adhesives Holdings, Inc. – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[27],[30],[37] | 6,140,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [27],[30],[37] | $ 2,895,000 |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[27],[30],[37] | 5.50% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[27],[30],[37] | 10.80% |  |  |  |  | 
| Investment, Identifier [Axis]: Edge Adhesives Holdings, Inc. – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[20],[31] |  |  | 6,140,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [20],[31] | $ 2,550,000 |  |  |  |  | 
| Ending Balance | [20],[31] |  |  | $ 2,550,000 |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[20],[31] |  |  | 5.50% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[20],[31] |  |  | 8.60% |  |  | 
| Investment, Identifier [Axis]: Edge Adhesives Holdings, Inc.—Preferred Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 5,466 |  |  |  |  | 
| Net Realized Gain (Loss) for Period |  | $ 0 |  |  |  |  | 
| Amount of Investment Income |  | 0 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 0 |  |  |  |  | 
| Gross Additions |  | 0 |  |  |  |  | 
| Gross Reductions |  | 0 |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 0 |  |  |  |  | 
| Ending Balance |  | 0 |  | $ 0 |  |  | 
| Investment, Identifier [Axis]: Edge Adhesives Holdings, Inc.—Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 6,140,000 |  |  |  |  | 
| Net Realized Gain (Loss) for Period |  | 0 |  |  |  |  | 
| Amount of Investment Income |  | (42,000) |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 2,550,000 |  |  |  |  | 
| Gross Additions |  | 0 |  |  |  |  | 
| Gross Reductions |  | 0 |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 345,000 |  |  |  |  | 
| Ending Balance |  | 2,895,000 |  | 2,550,000 |  |  | 
| Investment, Identifier [Axis]: Eegee’s LLC – Delayed Draw Term Loan |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 3,000,000 | [22],[23],[25] | 3,000,000 | [15],[17],[26] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | 2,910,000 |  |  |  |  | 
| Ending Balance |  | 2,865,000 | [25] | 2,910,000 | [26] |  | 
| Line of credit facility, available |  | $ 4,500,000 | [1],[2],[3],[5],[25] | $ 4,500,000 | [6],[7],[8],[10],[26] |  | 
| Investment, reference rate and spread |  | 7.80% | [1],[2],[3],[5],[25] | 8.30% | [6],[7],[8],[10],[26] |  | 
| Investment, interest rate, paid in cash |  | 13.10% | [1],[2],[3],[5],[25] | 11.40% | [6],[7],[8],[10],[26] |  | 
| Investment, Identifier [Axis]: Eegee’s LLC – Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | $ 0 | [22],[23],[25] | $ 0 | [15],[17],[26] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | 0 |  |  |  |  | 
| Ending Balance |  | 0 | [25] | 0 | [26] |  | 
| Line of credit facility, available |  | $ 1,000,000 | [1],[2],[3],[5],[25] | $ 1,000,000 | [6],[7],[8],[10],[26] |  | 
| Investment, reference rate and spread |  | 7.80% | [1],[2],[3],[5],[25] | 8.30% | [6],[7],[8],[10],[26] |  | 
| Investment, interest rate, paid in cash |  | 13.10% | [1],[2],[3],[5],[25] | 11.40% | [6],[7],[8],[10],[26] |  | 
| Investment, Identifier [Axis]: Eegee’s LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25] | $ 17,000,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25] | $ 16,235,000 |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[25] | 7.80% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25] | 13.10% |  |  |  |  | 
| Investment, Identifier [Axis]: Eegee’s LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[26] |  |  | $ 17,000,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | $ 16,490,000 |  |  |  |  | 
| Ending Balance | [26] |  |  | $ 16,490,000 |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[26] |  |  | 8.30% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[26] |  |  | 11.40% |  |  | 
| Investment, Identifier [Axis]: Encore Dredging Holdings, LLC – Delayed Draw Term Loan |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[26] |  |  | $ 5,023,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | 4,885,000 |  |  |  |  | 
| Ending Balance | [26] |  |  | $ 4,885,000 |  |  | 
| Investment, interest rate, paid in kind | [6],[7],[8],[10],[26] |  |  | 1.50% |  |  | 
| Line of credit facility, available | [6],[7],[8],[10],[26] |  |  | $ 0 |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[26] |  |  | 7.00% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[26] |  |  | 10.10% |  |  | 
| Investment, Identifier [Axis]: Encore Dredging Holdings, LLC – Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[26] |  |  | $ 0 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | $ 0 |  |  |  |  | 
| Ending Balance | [26] |  |  | 0 |  |  | 
| Line of credit facility, available | [6],[7],[8],[10],[26] |  |  | $ 3,000,000 |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[26] |  |  | 8.30% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[26] |  |  | 11.40% |  |  | 
| Investment, Identifier [Axis]: Encore Dredging Holdings, LLC – Preferred Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 3,840,000,000 | [22],[23],[27],[28] | 3,840,000 | [15],[17],[18],[20],[31] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20],[31] | $ 2,842,000 |  |  |  |  | 
| Ending Balance |  | 4,265,000 | [27],[28] | $ 2,842,000 | [18],[20],[31] |  | 
| Investment, Identifier [Axis]: Encore Dredging Holdings, LLC – Term Debt 1 |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[26] |  |  | 23,611,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | 22,962,000 |  |  |  |  | 
| Ending Balance | [26] |  |  | $ 22,962,000 |  |  | 
| Investment, interest rate, paid in kind | [6],[7],[8],[10],[26] |  |  | 1.50% |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[26] |  |  | 7.00% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[26] |  |  | 10.10% |  |  | 
| Investment, Identifier [Axis]: Encore Dredging Holdings, LLC – Term Debt 2 |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[26] |  |  | $ 4,532,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | 4,407,000 |  |  |  |  | 
| Ending Balance | [26] |  |  | $ 4,407,000 |  |  | 
| Investment, interest rate, paid in kind | [6],[7],[8],[10],[26] |  |  | 2.50% |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[26] |  |  | 7.00% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[26] |  |  | 10.10% |  |  | 
| Investment, Identifier [Axis]: Encore Dredging Holdings, LLC—Delayed Draw Term Loan |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 0 |  |  |  |  | 
| Net Realized Gain (Loss) for Period |  | 0 |  |  |  |  | 
| Amount of Investment Income |  | 700,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 4,885,000 |  |  |  |  | 
| Gross Additions |  | 78,000 |  |  |  |  | 
| Gross Reductions |  | (5,101,000) |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 138,000 |  |  |  |  | 
| Ending Balance |  | 0 |  | $ 4,885,000 |  |  | 
| Investment, Identifier [Axis]: Encore Dredging Holdings, LLC—Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 0 |  |  |  |  | 
| Net Realized Gain (Loss) for Period |  | 0 |  |  |  |  | 
| Amount of Investment Income |  | 75,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 0 |  |  |  |  | 
| Gross Additions |  | 0 |  |  |  |  | 
| Gross Reductions |  | 0 |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 0 |  |  |  |  | 
| Ending Balance |  | $ 0 |  | 0 |  |  | 
| Investment, Identifier [Axis]: Encore Dredging Holdings, LLC—Preferred Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 3,840,000 |  |  |  |  | 
| Net Realized Gain (Loss) for Period |  | $ 0 |  |  |  |  | 
| Amount of Investment Income |  | 0 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 2,842,000 |  |  |  |  | 
| Gross Additions |  | 0 |  |  |  |  | 
| Gross Reductions |  | 0 |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 1,423,000 |  |  |  |  | 
| Ending Balance |  | 4,265,000 |  | 2,842,000 |  |  | 
| Investment, Identifier [Axis]: Encore Dredging Holdings, LLC—Term Debt 1 |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 0 |  |  |  |  | 
| Net Realized Gain (Loss) for Period |  | 0 |  |  |  |  | 
| Amount of Investment Income |  | 3,293,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 22,962,000 |  |  |  |  | 
| Gross Additions |  | 362,000 |  |  |  |  | 
| Gross Reductions |  | (23,973,000) |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 649,000 |  |  |  |  | 
| Ending Balance |  | 0 |  | 22,962,000 |  |  | 
| Investment, Identifier [Axis]: Encore Dredging Holdings, LLC—Term Debt 2 |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 0 |  |  |  |  | 
| Net Realized Gain (Loss) for Period |  | 0 |  |  |  |  | 
| Amount of Investment Income |  | 727,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 4,407,000 |  |  |  |  | 
| Gross Additions |  | 116,000 |  |  |  |  | 
| Gross Reductions |  | (4,648,000) |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 125,000 |  |  |  |  | 
| Ending Balance |  | $ 0 |  | 4,407,000 |  |  | 
| Investment, Identifier [Axis]: Engineering Manufacturing Technologies, LLC – Common Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares | [22],[23],[27],[28] | 6,000,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [27],[28] | $ 0 |  |  |  |  | 
| Investment, Identifier [Axis]: Engineering Manufacturing Technologies, LLC – Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 0 | [22],[23],[25] | 0 | [15],[17],[26] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | 0 |  |  |  |  | 
| Ending Balance |  | 0 | [25] | 0 | [26] |  | 
| Line of credit facility, available |  | $ 3,000,000 | [1],[2],[3],[5],[25] | $ 3,000,000 | [6],[7],[8],[10],[26] |  | 
| Investment, reference rate and spread |  | 8.30% | [1],[2],[3],[5],[25] | 8.30% | [6],[7],[8],[10],[26] |  | 
| Investment, interest rate, paid in cash |  | 13.60% | [1],[2],[3],[5],[25] | 11.40% | [6],[7],[8],[10],[26] |  | 
| Investment, Identifier [Axis]: Engineering Manufacturing Technologies, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | $ 21,500,000 | [22],[23],[25] | $ 22,500,000 | [15],[17],[26] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | 22,134,000 |  |  |  |  | 
| Ending Balance |  | $ 19,726,000 | [25] | $ 22,134,000 | [26] |  | 
| Investment, reference rate and spread |  | 8.30% | [1],[2],[3],[5],[25] | 8.30% | [6],[7],[8],[10],[26] |  | 
| Investment, interest rate, paid in cash |  | 13.60% | [1],[2],[3],[5],[25] | 11.40% | [6],[7],[8],[10],[26] |  | 
| Investment, Identifier [Axis]: FES Resources Holdings LLC – Common Equity Units |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 6,233,000 | [22],[23],[27],[28] | 6,233 | [15],[17],[18],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 0 |  |  |  |  | 
| Ending Balance |  | $ 0 | [27],[28] | $ 0 | [18],[20] |  | 
| Investment, Identifier [Axis]: FES Resources Holdings LLC – Preferred Equity Units |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 6,350,000 | [22],[23],[27],[28] | 6,350 | [15],[17],[18],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 0 |  |  |  |  | 
| Ending Balance |  | 4,508,000 | [27],[28] | $ 0 | [18],[20] |  | 
| Investment, Identifier [Axis]: Fix-It Group, LLC – Delayed Draw Term Loan |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 6,911,000 | [22],[23],[25] | 0 | [15],[17],[26],[33] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26],[33] | 0 |  |  |  |  | 
| Ending Balance |  | 6,894,000 | [25] | 0 | [26],[33] |  | 
| Line of credit facility, available |  | $ 0 | [1],[2],[3],[5],[25] | $ 10,000,000 | [6],[7],[8],[10],[26],[33] |  | 
| Investment, reference rate and spread |  | 8.10% | [1],[2],[3],[5],[25] | 7.00% | [6],[7],[8],[10],[26],[33] |  | 
| Investment, interest rate, paid in cash |  | 13.40% | [1],[2],[3],[5],[25] | 10.10% | [6],[7],[8],[10],[26],[33] |  | 
| Investment, Identifier [Axis]: Fix-It Group, LLC – Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | $ 500,000 | [22],[23],[25] | $ 0 | [15],[17],[26],[33] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26],[33] | 0 |  |  |  |  | 
| Ending Balance |  | 499,000 | [25] | 0 | [26],[33] |  | 
| Line of credit facility, available |  | $ 2,500,000 | [1],[2],[3],[5],[25] | $ 3,000,000 | [6],[7],[8],[10],[26],[33] |  | 
| Investment, reference rate and spread |  | 8.10% | [1],[2],[3],[5],[25] | 7.00% | [6],[7],[8],[10],[26],[33] |  | 
| Investment, interest rate, paid in cash |  | 13.40% | [1],[2],[3],[5],[25] | 10.10% | [6],[7],[8],[10],[26],[33] |  | 
| Investment, Identifier [Axis]: Fix-It Group, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | $ 12,200,000 | [22],[23],[25] | $ 10,000,000 | [15],[17],[26],[33] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26],[33] | 9,950,000 |  |  |  |  | 
| Ending Balance |  | $ 12,170,000 | [25] | $ 9,950,000 | [26],[33] |  | 
| Investment, reference rate and spread |  | 8.10% | [1],[2],[3],[5],[25] | 7.00% | [6],[7],[8],[10],[26],[33] |  | 
| Investment, interest rate, paid in cash |  | 13.40% | [1],[2],[3],[5],[25] | 10.10% | [6],[7],[8],[10],[26],[33] |  | 
| Investment, Identifier [Axis]: Frontier Financial Group Inc. – Convertible Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | $ 198,000 | [22],[23],[27],[36] | $ 198,000 | [15],[17],[20],[38] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [20],[38] | 55,000 |  |  |  |  | 
| Ending Balance |  | $ 24,000 | [27],[36] | $ 55,000 | [20],[38] |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[20],[38] |  |  | 6.00% |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[27],[36] | 6.00% |  |  |  |  | 
| Investment, Identifier [Axis]: Frontier Financial Group Inc. – Preferred Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 766,000 | [22],[23],[27],[28] | 766 | [15],[17],[18],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 0 |  |  |  |  | 
| Ending Balance |  | $ 0 | [27],[28] | $ 0 | [18],[20] |  | 
| Investment, Identifier [Axis]: Frontier Financial Group Inc. – Preferred Stock Warrant |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 168,000 | [22],[23],[27],[28] | 168 | [15],[17],[18],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 0 |  |  |  |  | 
| Ending Balance |  | $ 0 | [27],[28] | $ 0 | [18],[20] |  | 
| Investment, Identifier [Axis]: Funko Acquisition Holdings, LLC(S) – Common Units |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 4,239,000 | [22],[23],[28],[30],[39] | 4,239 | [15],[17],[18],[31],[40] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[31],[40] | $ 58,000 |  |  |  |  | 
| Ending Balance |  | $ 22,000 | [28],[30],[39] | $ 58,000 | [18],[31],[40] |  | 
| Investment, Identifier [Axis]: GFRC 360, LLC – Common Stock Warrants |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Units |  | 45.00% | [22],[23],[27],[28] | 45.00% | [15],[17],[18],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 0 |  |  |  |  | 
| Ending Balance |  | 0 | [27],[28] | $ 0 | [18],[20] |  | 
| Investment, Identifier [Axis]: GFRC 360, LLC – Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 1,275,000 | [22],[23],[25] | 700,000 | [15],[17],[26] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | 681,000 |  |  |  |  | 
| Ending Balance |  | 1,205,000 | [25] | 681,000 | [26] |  | 
| Line of credit facility, available |  | $ 175,000 | [1],[2],[3],[5],[25] | $ 500,000 | [6],[7],[8],[10],[26] |  | 
| Investment, reference rate and spread |  | 8.00% | [1],[2],[3],[5],[25] | 8.00% | [6],[7],[8],[10],[26] |  | 
| Investment, interest rate, paid in cash |  | 13.30% | [1],[2],[3],[5],[25] | 11.10% | [6],[7],[8],[10],[26] |  | 
| Investment, Identifier [Axis]: GFRC 360, LLC – Preferred Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 1,000,000 | [22],[23],[27],[28] | 1,000 | [15],[17],[18],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 551,000 |  |  |  |  | 
| Ending Balance |  | 253,000 | [27],[28] | $ 551,000 | [18],[20] |  | 
| Investment, Identifier [Axis]: GFRC 360, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 1,000,000 | [22],[23],[25] | 1,000,000 | [15],[17],[26] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | 973,000 |  |  |  |  | 
| Ending Balance |  | $ 945,000 | [25] | $ 973,000 | [26] |  | 
| Investment, reference rate and spread |  | 8.00% | [1],[2],[3],[5],[25] | 8.00% | [6],[7],[8],[10],[26] |  | 
| Investment, interest rate, paid in cash |  | 13.30% | [1],[2],[3],[5],[25] | 11.10% | [6],[7],[8],[10],[26] |  | 
| Investment, Identifier [Axis]: GSM MidCo LLC – Common Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 767,000 | [22],[23],[27],[28] | 767 | [15],[17],[18],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 1,359,000 |  |  |  |  | 
| Ending Balance |  | 1,562,000 | [27],[28] | $ 1,359,000 | [18],[20] |  | 
| Investment, Identifier [Axis]: Giving Home Health Care, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 28,800,000 | [22],[23],[25],[36] | 28,800,000 | [15],[17],[26],[38] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26],[38] | 28,800,000 |  |  |  |  | 
| Ending Balance |  | $ 28,800,000 | [25],[36] | $ 28,800,000 | [26],[38] |  | 
| Investment, interest rate, paid in cash |  | 12.50% | [1],[2],[3],[5],[25],[36] | 12.50% | [6],[7],[8],[10],[26],[38] |  | 
| Investment, Identifier [Axis]: Giving Home Health Care, LLC – Warrant |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 10,667,000 | [22],[23],[27],[28] | 10,667 | [15],[17],[18],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 19,000 |  |  |  |  | 
| Ending Balance |  | 2,794,000 | [27],[28] | $ 19,000 | [18],[20] |  | 
| Investment, Identifier [Axis]: Gray Matter Systems, LLC – Delayed Draw Term Loan |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[26],[38] |  |  | 2,500,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26],[38] | 2,481,000 |  |  |  |  | 
| Ending Balance | [26],[38] |  |  | 2,481,000 |  |  | 
| Line of credit facility, available | [6],[7],[8],[10],[26],[38] |  |  | $ 4,000,000 |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[26],[38] |  |  | 11.30% |  |  | 
| Investment, Identifier [Axis]: Gray Matter Systems, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 13,645,000 | [22],[23],[25],[36] | $ 2,100,000 | [15],[17],[26],[38] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26],[38] | 2,084,000 |  |  |  |  | 
| Ending Balance |  | $ 13,645,000 | [25],[36] | $ 2,084,000 | [26],[38] |  | 
| Investment, interest rate, paid in kind | [1],[2],[3],[5],[25],[36] | 2.00% |  |  |  |  | 
| Investment, interest rate, paid in cash |  | 12.00% | [1],[2],[3],[5],[25],[36] | 11.30% | [6],[7],[8],[10],[26],[38] |  | 
| Investment, Identifier [Axis]: HH-Inspire Acquisition, Inc. – Delayed Draw Term Loan |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[26],[33] |  |  | $ 10,000,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26],[33] | $ 9,925,000 |  |  |  |  | 
| Ending Balance | [26],[33] |  |  | 9,925,000 |  |  | 
| Line of credit facility, available | [6],[7],[8],[10],[26],[33] |  |  | $ 0 |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[26],[33] |  |  | 6.80% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[26],[33] |  |  | 9.90% |  |  | 
| Investment, Identifier [Axis]: HH-Inspire Acquisition, Inc. – Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 1,359,000 | [22],[23],[25],[32] | $ 1,500,000 | [15],[17],[26],[33] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26],[33] | 1,489,000 |  |  |  |  | 
| Ending Balance |  | 1,347,000 | [25],[32] | 1,489,000 | [26],[33] |  | 
| Line of credit facility, available |  | $ 478,000 | [1],[2],[3],[5],[25],[32] | $ 1,500,000 | [6],[7],[8],[10],[26],[33] |  | 
| Investment, reference rate and spread |  | 8.00% | [1],[2],[3],[5],[25],[32] | 6.80% | [6],[7],[8],[10],[26],[33] |  | 
| Investment, interest rate, paid in cash |  | 13.40% | [1],[2],[3],[5],[25],[32] | 9.90% | [6],[7],[8],[10],[26],[33] |  | 
| Investment, Identifier [Axis]: HH-Inspire Acquisition, Inc. – Preferred Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 1,329,054,000 | [22],[23],[27],[28] | 854,848 | [15],[17],[18],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 945,000 |  |  |  |  | 
| Ending Balance |  | 3,451,000 | [27],[28] | $ 945,000 | [18],[20] |  | 
| Investment, Identifier [Axis]: HH-Inspire Acquisition, Inc. – Term Debt 1 |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 16,013,000 | [22],[23],[25],[32] | 16,000,000 | [15],[17],[26],[33] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26],[33] | 15,880,000 |  |  |  |  | 
| Ending Balance |  | $ 15,872,000 | [25],[32] | $ 15,880,000 | [26],[33] |  | 
| Investment, reference rate and spread |  | 8.00% | [1],[2],[3],[5],[25],[32] | 6.80% | [6],[7],[8],[10],[26],[33] |  | 
| Investment, interest rate, paid in cash |  | 13.40% | [1],[2],[3],[5],[25],[32] | 9.90% | [6],[7],[8],[10],[26],[33] |  | 
| Investment, Identifier [Axis]: HH-Inspire Acquisition, Inc. – Term Debt 2 |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | $ 3,225,000 | [22],[23],[25],[32] | $ 8,000,000 | [15],[17],[26],[33] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26],[33] | 7,940,000 |  |  |  |  | 
| Ending Balance |  | $ 3,197,000 | [25],[32] | $ 7,940,000 | [26],[33] |  | 
| Investment, reference rate and spread |  | 8.00% | [1],[2],[3],[5],[25],[32] | 6.80% | [6],[7],[8],[10],[26],[33] |  | 
| Investment, interest rate, paid in cash |  | 13.40% | [1],[2],[3],[5],[25],[32] | 9.90% | [6],[7],[8],[10],[26],[33] |  | 
| Investment, Identifier [Axis]: Imperative Holdings Corporation – Preferred Equity Units |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 972,569,000 | [22],[23],[27],[28] | 1,474,225 | [15],[17],[18],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 2,028,000 |  |  |  |  | 
| Ending Balance |  | 2,318,000 | [27],[28] | $ 2,028,000 | [18],[20] |  | 
| Investment, Identifier [Axis]: Imperative Holdings Corporation – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25] | 21,015,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25] | $ 20,858,000 |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[25] | 9.80% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25] | 15.10% |  |  |  |  | 
| Investment, Identifier [Axis]: Imperative Holdings Corporation – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[26] |  |  | 24,016,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | $ 23,295,000 |  |  |  |  | 
| Ending Balance | [26] |  |  | $ 23,295,000 |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[26] |  |  | 10.30% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[26] |  |  | 13.40% |  |  | 
| Investment, Identifier [Axis]: LWO Acquisitions Company LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[20],[41] |  |  | $ 95,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [20],[41] | 0 |  |  |  |  | 
| Ending Balance | [20],[41] |  |  | 0 |  |  | 
| Investment, Identifier [Axis]: LWO Acquisitions Company LLC—Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 0 |  |  |  |  | 
| Net Realized Gain (Loss) for Period |  | (95,000) |  |  |  |  | 
| Amount of Investment Income |  | 0 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 0 |  |  |  |  | 
| Gross Additions |  | 0 |  |  |  |  | 
| Gross Reductions |  | (95,000) |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 95,000 |  |  |  |  | 
| Ending Balance |  | 0 |  | 0 |  |  | 
| Investment, Identifier [Axis]: Leadpoint Business Services, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25] | 13,500,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25] | $ 13,399,000 |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[25] | 8.50% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25] | 13.80% |  |  |  |  | 
| Investment, Identifier [Axis]: Leeds Novamark Capital I, L.P. – Limited Partnership Interest |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Units | [22],[23],[28],[42],[43] | 3.50% |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [28],[42],[43] | $ 231,000 |  |  |  |  | 
| Line of credit facility, available | [1],[2],[3],[5],[28],[42],[43] | 843,000 |  |  |  |  | 
| Investment, Identifier [Axis]: Lonestar EMS, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[27],[36] | 3,927,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [27],[36] | $ 3,927,000 |  |  |  |  | 
| Investment, interest rate, paid in kind | [1],[2],[3],[5],[27],[36] | 8.00% |  |  |  |  | 
| Investment, Identifier [Axis]: Lonestar EMS, LLC - Common Units |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Units |  | 100.00% |  |  |  |  | 
| Net Realized Gain (Loss) for Period |  | $ 0 |  |  |  |  | 
| Amount of Investment Income |  | 0 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 0 |  |  |  |  | 
| Gross Additions |  | 0 |  |  |  |  | 
| Gross Reductions |  | 0 |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 0 |  |  |  |  | 
| Ending Balance |  | $ 0 |  | $ 0 |  |  | 
| Investment, Identifier [Axis]: Lonestar EMS, LLC – Common Units |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Units |  | 100.00% | [22],[23],[27],[28] | 100.00% | [15],[17],[18],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 0 |  |  |  |  | 
| Ending Balance |  | 0 | [27],[28] | $ 0 | [18],[20] |  | 
| Investment, Identifier [Axis]: Lonestar EMS, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[20],[38] |  |  | 3,250,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [20],[38] | 3,030,000 |  |  |  |  | 
| Ending Balance | [20],[38] |  |  | $ 3,030,000 |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[20],[38] |  |  | 8.00% |  |  | 
| Investment, Identifier [Axis]: Lonestar EMS, LLC—Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 3,927,000 |  |  |  |  | 
| Net Realized Gain (Loss) for Period |  | 0 |  |  |  |  | 
| Amount of Investment Income |  | 302,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 3,030,000 |  |  |  |  | 
| Gross Additions |  | 677,000 |  |  |  |  | 
| Gross Reductions |  | 0 |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 220,000 |  |  |  |  | 
| Ending Balance |  | 3,927,000 |  | $ 3,030,000 |  |  | 
| Investment, Identifier [Axis]: MCG Energy Solutions, LLC – Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[26] |  |  | 0 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | $ 0 |  |  |  |  | 
| Ending Balance | [26] |  |  | 0 |  |  | 
| Line of credit facility, available | [6],[7],[8],[10],[26] |  |  | $ 3,000,000 |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[26] |  |  | 7.50% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[26] |  |  | 10.60% |  |  | 
| Investment, Identifier [Axis]: MCG Energy Solutions, LLC – Preferred Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 7,000,000,000 | [22],[23],[27],[28] | 7,000,000 | [15],[17],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [20] | $ 8,151,000 |  |  |  |  | 
| Ending Balance |  | 8,904,000 | [27],[28] | $ 8,151,000 | [20] |  | 
| Investment, Identifier [Axis]: MCG Energy Solutions, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25] | 20,146,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25] | $ 17,628,000 |  |  |  |  | 
| Investment, interest rate, paid in kind | [1],[2],[3],[5],[25] | 3.50% |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[25] | 7.60% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25] | 12.90% |  |  |  |  | 
| Investment, Identifier [Axis]: MCG Energy Solutions, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[26] |  |  | 20,820,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | $ 19,779,000 |  |  |  |  | 
| Ending Balance | [26] |  |  | $ 19,779,000 |  |  | 
| Investment, interest rate, paid in kind | [6],[7],[8],[10],[26] |  |  | 3.50% |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[26] |  |  | 7.50% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[26] |  |  | 10.60% |  |  | 
| Investment, Identifier [Axis]: NeoGraf Solutions LLC – Common Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares | [22],[23],[27],[28] | 2,000,000,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [27],[28] | $ 0 |  |  |  |  | 
| Investment, Identifier [Axis]: NeoGraf Solutions LLC – Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25] | 0 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25] | $ 0 |  |  |  |  | 
| Investment, interest rate, paid in kind | [1],[2],[3],[5],[25] | 1.30% |  |  |  |  | 
| Line of credit facility, available | [1],[2],[3],[5],[25] | $ 4,500,000 |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[25] | 7.00% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25] | 11.00% |  |  |  |  | 
| Investment, Identifier [Axis]: NeoGraf Solutions LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25] | $ 27,154,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25] | $ 26,000,000 |  |  |  |  | 
| Investment, interest rate, paid in kind | [1],[2],[3],[5],[25] | 1.30% |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[25] | 7.00% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25] | 11.00% |  |  |  |  | 
| Investment, Identifier [Axis]: NetFortris Corp. – Preferred Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares | [15],[17],[18],[20] |  |  | 7,890,860 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 469,000 |  |  |  |  | 
| Ending Balance | [18],[20] |  |  | $ 469,000 |  |  | 
| Investment, Identifier [Axis]: OCI, LLC – Common Units |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares | [22],[23],[27],[28] | 306,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [27],[28] | $ 0 |  |  |  |  | 
| Investment, Identifier [Axis]: OCI, LLC – Term Debt 1 |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25] | 20,000,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25] | $ 19,800,000 |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[25] | 7.50% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25] | 12.80% |  |  |  |  | 
| Investment, Identifier [Axis]: OCI, LLC – Term Debt 2 |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25],[36] | $ 2,012,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25],[36] | $ 1,992,000 |  |  |  |  | 
| Investment, interest rate, paid in kind | [1],[2],[3],[5],[25],[36] | 7.00% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25],[36] | 7.00% |  |  |  |  | 
| Investment, Identifier [Axis]: Ohio Armor Holdings, LLC – Common Equity |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares | [22],[23],[27],[28] | 100,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [27],[28] | $ 680,000 |  |  |  |  | 
| Investment, Identifier [Axis]: Ohio Armor Holdings, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 17,738,000 | [22],[23],[25] | 18,913,000 | [15],[17],[26] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | 18,558,000 |  |  |  |  | 
| Ending Balance |  | $ 17,294,000 | [25] | $ 18,558,000 | [26] |  | 
| Investment, reference rate and spread |  | 8.00% | [1],[2],[3],[5],[25] | 8.00% | [6],[7],[8],[10],[26] |  | 
| Investment, interest rate, paid in cash |  | 13.30% | [1],[2],[3],[5],[25] | 11.10% | [6],[7],[8],[10],[26] |  | 
| Investment, Identifier [Axis]: PIC 360, LLC – Common Equity Units |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 750,000 | [22],[23],[27],[28] | 750 | [15],[17],[18],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 3,454,000 |  |  |  |  | 
| Ending Balance |  | $ 284,000 | [27],[28] | $ 3,454,000 | [18],[20] |  | 
| Investment, Identifier [Axis]: PIC 360, LLC—Common Equity Units |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 750 |  |  |  |  | 
| Net Realized Gain (Loss) for Period |  | $ 3,700,000 |  |  |  |  | 
| Amount of Investment Income |  | 691,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 3,454,000 |  |  |  |  | 
| Gross Additions |  | 0 |  |  |  |  | 
| Gross Reductions |  | 0 |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | (3,170,000) |  |  |  |  | 
| Ending Balance |  | 284,000 |  | 3,454,000 |  |  | 
| Investment, Identifier [Axis]: Pansophic Learning, Ltd. – Term Debt 1 |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 28,000,000 | [22],[23],[25],[32] | 28,000,000 | [15],[17],[26] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | 27,825,000 |  |  |  |  | 
| Ending Balance |  | $ 27,965,000 | [25],[32] | $ 27,825,000 | [26] |  | 
| Investment, reference rate and spread |  | 7.50% | [1],[2],[3],[5],[25],[32] | 7.30% | [6],[7],[8],[10],[26] |  | 
| Investment, interest rate, paid in cash |  | 12.90% | [1],[2],[3],[5],[25],[32] | 10.40% | [6],[7],[8],[10],[26] |  | 
| Investment, Identifier [Axis]: Pansophic Learning, Ltd. – Term Debt 2 |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | $ 5,000,000 | [22],[23],[25],[32] | $ 5,000,000 | [15],[17],[26] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | 4,969,000 |  |  |  |  | 
| Ending Balance |  | $ 4,994,000 | [25],[32] | $ 4,969,000 | [26] |  | 
| Investment, reference rate and spread |  | 7.50% | [1],[2],[3],[5],[25],[32] | 7.30% | [6],[7],[8],[10],[26] |  | 
| Investment, interest rate, paid in cash |  | 12.90% | [1],[2],[3],[5],[25],[32] | 10.40% | [6],[7],[8],[10],[26] |  | 
| Investment, Identifier [Axis]: R2i Holdings, LLC – Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[38],[44] |  |  | $ 829,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [38],[44] | $ 829,000 |  |  |  |  | 
| Ending Balance | [38],[44] |  |  | $ 829,000 |  |  | 
| Investment, interest rate, paid in kind | [6],[7],[8],[10],[38],[44] |  |  | 8.00% |  |  | 
| Line of credit facility, available | [6],[7],[8],[10],[38],[44] |  |  | $ 1,171,000 |  |  | 
| Investment, Identifier [Axis]: R2i Holdings, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[38],[44] |  |  | 18,000,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [38],[44] | $ 18,000,000 |  |  |  |  | 
| Ending Balance | [38],[44] |  |  | $ 18,000,000 |  |  | 
| Investment, interest rate, paid in kind | [6],[7],[8],[10],[38],[44] |  |  | 8.00% |  |  | 
| Investment, Identifier [Axis]: Salt & Straw, LLC – Common Warrant |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Units | [22],[23],[27],[28] | 0.40% |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [27],[28] | $ 31,000 |  |  |  |  | 
| Investment, Identifier [Axis]: Salt & Straw, LLC – Delayed Draw Term Loan |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 10,200,000 | [22],[23],[25] | $ 0 | [15],[17],[26] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | 0 |  |  |  |  | 
| Ending Balance |  | 9,715,000 | [25] | 0 | [26] |  | 
| Line of credit facility, available |  | $ 1,300,000 | [1],[2],[3],[5],[25] | $ 11,500,000 | [6],[7],[8],[10],[26] |  | 
| Investment, reference rate and spread |  | 9.10% | [1],[2],[3],[5],[25] | 8.00% | [6],[7],[8],[10],[26] |  | 
| Investment, interest rate, paid in cash |  | 14.40% | [1],[2],[3],[5],[25] | 11.10% | [6],[7],[8],[10],[26] |  | 
| Investment, Identifier [Axis]: Salt & Straw, LLC – Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | $ 0 | [22],[23],[25] | $ 800,000 | [15],[17],[26] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | 800,000 |  |  |  |  | 
| Ending Balance |  | 0 | [25] | 800,000 | [26] |  | 
| Line of credit facility, available |  | $ 2,000,000 | [1],[2],[3],[5],[25] | $ 1,200,000 | [6],[7],[8],[10],[26] |  | 
| Investment, reference rate and spread |  | 9.10% | [1],[2],[3],[5],[25] | 8.00% | [6],[7],[8],[10],[26] |  | 
| Investment, interest rate, paid in cash |  | 14.40% | [1],[2],[3],[5],[25] | 11.10% | [6],[7],[8],[10],[26] |  | 
| Investment, Identifier [Axis]: Salvo Technologies, Inc. – Preferred Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 2,500,000 | [22],[23],[27],[28] | 2,500 | [15],[17],[18],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 2,584,000 |  |  |  |  | 
| Ending Balance |  | 1,225,000 | [27],[28] | $ 2,584,000 | [18],[20] |  | 
| Investment, Identifier [Axis]: Salvo Technologies, Inc. – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 11,768,000 | [22],[23],[25] | 11,887,000 | [15],[17],[26],[29] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26],[29] | 11,619,000 |  |  |  |  | 
| Ending Balance |  | $ 10,900,000 | [25] | $ 11,619,000 | [26],[29] |  | 
| Investment, reference rate and spread |  | 9.50% | [1],[2],[3],[5],[25] | 9.50% | [6],[7],[8],[10],[26],[29] |  | 
| Investment, interest rate, paid in cash |  | 14.80% | [1],[2],[3],[5],[25] | 12.50% | [6],[7],[8],[10],[26],[29] |  | 
| Investment, Identifier [Axis]: Sea Link International IRB, Inc. – Preferred Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 98,039,000 | [22],[23],[27],[28] | 98,039 | [15],[17],[18],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 153,000 |  |  |  |  | 
| Ending Balance |  | 183,000 | [27],[28] | $ 153,000 | [18],[20] |  | 
| Investment, Identifier [Axis]: Sea Link International IRB, Inc. – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[26],[38] |  |  | 11,719,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26],[38] | 11,074,000 |  |  |  |  | 
| Ending Balance | [26],[38] |  |  | $ 11,074,000 |  |  | 
| Investment, interest rate, paid in kind | [6],[7],[8],[10],[26],[38] |  |  | 14.50% |  |  | 
| Investment, Identifier [Axis]: Sea Link International IRB, Inc. – Term Debt 1 |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25],[36] | 12,083,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25],[36] | $ 11,675,000 |  |  |  |  | 
| Investment, interest rate, paid in kind | [1],[2],[3],[5],[25],[36] | 2.00% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25],[36] | 11.30% |  |  |  |  | 
| Investment, Identifier [Axis]: Sea Link International IRB, Inc. – Term Debt 2 |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25],[36] | $ 4,000,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25],[36] | $ 4,000,000 |  |  |  |  | 
| Investment, interest rate, paid in kind | [1],[2],[3],[5],[25],[36] | 2.00% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25],[36] | 12.00% |  |  |  |  | 
| Investment, Identifier [Axis]: Sea Link International IRB, Inc.– Common Equity Units |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 823,333,000 | [22],[23],[27],[28] | 823,333 | [15],[17],[18],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 105,000 |  |  |  |  | 
| Ending Balance |  | $ 340,000 | [27],[28] | $ 105,000 | [18],[20] |  | 
| Investment, Identifier [Axis]: Sokol & Company Holdings, LLC – Common Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 1,500,000,000 | [22],[23],[27],[28] | 1,500,000 | [15],[17],[18],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 1,500,000 |  |  |  |  | 
| Ending Balance |  | 1,612,000 | [27],[28] | $ 1,500,000 | [18],[20] |  | 
| Investment, Identifier [Axis]: Sokol & Company Holdings, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[26],[29] |  |  | 13,500,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26],[29] | 13,500,000 |  |  |  |  | 
| Ending Balance | [26],[29] |  |  | $ 13,500,000 |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[26],[29] |  |  | 7.00% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[26],[29] |  |  | 10.00% |  |  | 
| Investment, Identifier [Axis]: Sokol & Company Holdings, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25] | 13,500,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25] | $ 13,095,000 |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[25] | 7.00% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25] | 12.30% |  |  |  |  | 
| Investment, Identifier [Axis]: SpaceCo Holdings, LLC – Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | $ 1,450,000 | [22],[23],[25],[32] | $ 1,900,000 | [15],[17],[26],[33] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26],[33] | 1,886,000 |  |  |  |  | 
| Ending Balance |  | 1,434,000 | [25],[32] | 1,886,000 | [26],[33] |  | 
| Line of credit facility, available |  | $ 550,000 | [1],[2],[3],[5],[25],[32] | $ 100,000 | [6],[7],[8],[10],[26],[33] |  | 
| Investment, reference rate and spread |  | 7.20% | [1],[2],[3],[5],[25],[32] | 7.00% | [6],[7],[8],[10],[26],[33] |  | 
| Investment, interest rate, paid in cash |  | 12.50% | [1],[2],[3],[5],[25],[32] | 10.80% | [6],[7],[8],[10],[26],[33] |  | 
| Investment, Identifier [Axis]: SpaceCo Holdings, LLC – Term Deb |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[26],[33] |  |  | $ 31,719,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26],[33] | $ 31,481,000 |  |  |  |  | 
| Ending Balance | [26],[33] |  |  | $ 31,481,000 |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[26],[33] |  |  | 7.00% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[26],[33] |  |  | 10.80% |  |  | 
| Investment, Identifier [Axis]: SpaceCo Holdings, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25],[32] | 30,284,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25],[32] | $ 29,944,000 |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[25],[32] | 7.20% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25],[32] | 12.50% |  |  |  |  | 
| Investment, Identifier [Axis]: Springfield, Inc. – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | $ 30,000,000 | [22],[23],[25] | $ 30,000,000 | [15],[17],[26] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | 29,738,000 |  |  |  |  | 
| Ending Balance |  | $ 29,850,000 | [25] | $ 29,738,000 | [26] |  | 
| Investment, reference rate and spread |  | 10.10% | [1],[2],[3],[5],[25] | 10.00% | [6],[7],[8],[10],[26] |  | 
| Investment, interest rate, paid in cash |  | 15.40% | [1],[2],[3],[5],[25] | 13.10% | [6],[7],[8],[10],[26] |  | 
| Investment, Identifier [Axis]: TNCP Intermediate HoldCo, LLC – Common Equity Units |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 790,000,000 | [22],[23],[27],[28] | 790,000 | [15],[17],[18],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 2,337,000 |  |  |  |  | 
| Ending Balance |  | 3,073,000 | [27],[28] | $ 2,337,000 | [18],[20] |  | 
| Investment, Identifier [Axis]: TNCP Intermediate HoldCo, LLC – Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 900,000 | [22],[23],[27],[36] | 1,000,000 | [15],[17],[20],[38] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [20],[38] | 1,000,000 |  |  |  |  | 
| Ending Balance |  | 900,000 | [27],[36] | 1,000,000 | [20],[38] |  | 
| Line of credit facility, available | [6],[7],[8],[10],[20],[38] |  |  | $ 1,000,000 |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[20],[38] |  |  | 8.00% |  |  | 
| Investment, Identifier [Axis]: TNCP Intermediate HoldCo, LLC—-Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 900,000 |  |  |  |  | 
| Net Realized Gain (Loss) for Period |  | 0 |  |  |  |  | 
| Amount of Investment Income |  | 75,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 1,000,000 |  |  |  |  | 
| Gross Additions |  | 0 |  |  |  |  | 
| Gross Reductions |  | (100,000) |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 0 |  |  |  |  | 
| Ending Balance |  | 900,000 |  | $ 1,000,000 |  |  | 
| Line of credit facility, available | [1],[2],[3],[5],[27],[36] | $ 1,100,000 |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[27],[36] | 8.00% |  |  |  |  | 
| Investment, Identifier [Axis]: TNCP Intermediate HoldCo, LLC—Common Equity Units |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 790,000 |  |  |  |  | 
| Net Realized Gain (Loss) for Period |  | $ 0 |  |  |  |  | 
| Amount of Investment Income |  | 0 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 2,337,000 |  |  |  |  | 
| Gross Additions |  | 0 |  |  |  |  | 
| Gross Reductions |  | 0 |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 736,000 |  |  |  |  | 
| Ending Balance |  | 3,073,000 |  | 2,337,000 |  |  | 
| Investment, Identifier [Axis]: Tailwind Smith Cooper Intermediate Corporation – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 5,000,000 | [21],[22],[23],[32] | 5,000,000 | [15],[17],[24] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [24] | 4,313,000 |  |  |  |  | 
| Ending Balance |  | $ 4,294,000 | [21],[32] | $ 4,313,000 | [24] |  | 
| Investment, reference rate and spread |  | 9.00% | [1],[2],[3],[5],[21],[32] | 9.00% | [6],[7],[8],[10],[24] |  | 
| Investment, interest rate, paid in cash |  | 14.40% | [1],[2],[3],[5],[21],[32] | 12.10% | [6],[7],[8],[10],[24] |  | 
| Investment, Identifier [Axis]: Targus Cayman HoldCo, Ltd. – Common Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares | [15],[17],[18],[44],[45] |  |  | 3,076,414 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[44],[45] | $ 7,978,000 |  |  |  |  | 
| Ending Balance | [18],[44],[45] |  |  | $ 7,978,000 |  |  | 
| Investment, Identifier [Axis]: Technical Resource Management, LLC – Common Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares | [22],[23],[27],[28] | 2,000,000,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [27],[28] | $ 1,415,000 |  |  |  |  | 
| Investment, Identifier [Axis]: Technical Resource Management, LLC – Delayed Draw Term Loan |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25] | 0 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25] | 0 |  |  |  |  | 
| Line of credit facility, available | [1],[2],[3],[5],[25] | $ 2,500,000 |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[25] | 8.00% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25] | 13.30% |  |  |  |  | 
| Investment, Identifier [Axis]: Technical Resource Management, LLC – Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25] | $ 2,000,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25] | 1,970,000 |  |  |  |  | 
| Line of credit facility, available | [1],[2],[3],[5],[25] | $ 1,000,000 |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[25] | 8.00% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25] | 13.30% |  |  |  |  | 
| Investment, Identifier [Axis]: Technical Resource Management, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25] | $ 23,000,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25] | $ 22,655,000 |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[25] | 8.00% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25] | 13.30% |  |  |  |  | 
| Investment, Identifier [Axis]: Total Safety Holdings, LLC – Common Equity |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 435,000 | [22],[23],[27],[28] | 435 | [15],[17],[18],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 50,000 |  |  |  |  | 
| Ending Balance |  | $ 146,000 | [27],[28] | $ 50,000 | [18],[20] |  | 
| Investment, Identifier [Axis]: Triple H Food Processors, LLC – Common Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 250,000,000 | [22],[23],[27],[28] | 250,000 | [15],[17],[18],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 672,000 |  |  |  |  | 
| Ending Balance |  | $ 1,641,000 | [27],[28] | $ 672,000 | [18],[20] |  | 
| Investment, Identifier [Axis]: Triple H Food Processors, LLC – Preferred Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 75,000 | [22],[23],[27],[28] | 75 | [15],[17],[18],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 120,000 |  |  |  |  | 
| Ending Balance |  | 141,000 | [27],[28] | $ 120,000 | [18],[20] |  | 
| Investment, Identifier [Axis]: Trowbridge Chicago, LLC – Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25] | 0 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25] | 0 |  |  |  |  | 
| Line of credit facility, available | [1],[2],[3],[5],[25] | $ 2,000,000 |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[25] | 7.00% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25] | 12.30% |  |  |  |  | 
| Investment, Identifier [Axis]: Trowbridge Chicago, LLC – Preferred Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares | [22],[23],[27],[28] | 242,105,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [27],[28] | $ 750,000 |  |  |  |  | 
| Investment, Identifier [Axis]: Trowbridge Chicago, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25] | 5,750,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25] | $ 5,664,000 |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[25] | 7.00% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25] | 12.30% |  |  |  |  | 
| Investment, Identifier [Axis]: Turn Key Health Clinics, LLC – Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | $ 500,000 | [22],[23],[25] | 500,000 | [15],[17],[26] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | 495,000 |  |  |  |  | 
| Ending Balance |  | 499,000 | [25] | 495,000 | [26] |  | 
| Line of credit facility, available |  | $ 1,500,000 | [1],[2],[3],[5],[25] | $ 1,500,000 | [6],[7],[8],[10],[26] |  | 
| Investment, reference rate and spread |  | 7.30% | [1],[2],[3],[5],[25] | 7.30% | [6],[7],[8],[10],[26] |  | 
| Investment, interest rate, paid in cash |  | 12.60% | [1],[2],[3],[5],[25] | 10.40% | [6],[7],[8],[10],[26] |  | 
| Investment, Identifier [Axis]: Turn Key Health Clinics, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | $ 11,000,000 | [22],[23],[25] | $ 11,000,000 | [15],[17],[26] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | 10,890,000 |  |  |  |  | 
| Ending Balance |  | $ 10,986,000 | [25] | $ 10,890,000 | [26] |  | 
| Investment, reference rate and spread |  | 7.30% | [1],[2],[3],[5],[25] | 7.30% | [6],[7],[8],[10],[26] |  | 
| Investment, interest rate, paid in cash |  | 12.60% | [1],[2],[3],[5],[25] | 10.40% | [6],[7],[8],[10],[26] |  | 
| Investment, Identifier [Axis]: Unirac Holdings, Inc. – Delayed Draw Term Loan |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | $ 1,108,000 | [22],[23],[25] | $ 0 | [15],[17],[26],[29] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26],[29] | 0 |  |  |  |  | 
| Ending Balance |  | 1,111,000 | [25] | 0 | [26],[29] |  | 
| Line of credit facility, available |  | $ 1,669,000 | [1],[2],[3],[5],[25] | $ 2,778,000 | [6],[7],[8],[10],[26],[29] |  | 
| Investment, reference rate and spread |  | 6.50% | [1],[2],[3],[5],[25] | 6.50% | [6],[7],[8],[10],[26],[29] |  | 
| Investment, interest rate, paid in cash |  | 11.80% | [1],[2],[3],[5],[25] | 9.50% | [6],[7],[8],[10],[26],[29] |  | 
| Investment, Identifier [Axis]: Unirac Holdings, Inc. – Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | $ 978,000 | [22],[23],[25] | $ 0 | [15],[17],[26],[29] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26],[29] | 0 |  |  |  |  | 
| Ending Balance |  | 980,000 | [25] | 0 | [26],[29] |  | 
| Line of credit facility, available |  | $ 1,244,000 | [1],[2],[3],[5],[25] | $ 2,222,000 | [6],[7],[8],[10],[26],[29] |  | 
| Investment, reference rate and spread |  | 6.50% | [1],[2],[3],[5],[25] | 6.50% | [6],[7],[8],[10],[26],[29] |  | 
| Investment, interest rate, paid in cash |  | 11.80% | [1],[2],[3],[5],[25] | 9.50% | [6],[7],[8],[10],[26],[29] |  | 
| Investment, Identifier [Axis]: Unirac Holdings, Inc. – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25] | $ 14,888,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25] | $ 14,925,000 |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[25] | 6.50% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25] | 11.80% |  |  |  |  | 
| Investment, Identifier [Axis]: Unirac Holdings, Inc. – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[26],[29] |  |  | $ 15,000,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26],[29] | $ 15,000,000 |  |  |  |  | 
| Ending Balance | [26],[29] |  |  | $ 15,000,000 |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[26],[29] |  |  | 6.50% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[26],[29] |  |  | 9.50% |  |  | 
| Investment, Identifier [Axis]: Viva Railings, LLC – Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 0 | [22],[23],[25] | $ 0 | [15],[17],[26] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | 0 |  |  |  |  | 
| Ending Balance |  | 0 | [25] | 0 | [26] |  | 
| Line of credit facility, available |  | $ 4,000,000 | [1],[2],[3],[5],[25] | $ 4,000,000 | [6],[7],[8],[10],[26] |  | 
| Investment, reference rate and spread |  | 7.10% | [1],[2],[3],[5],[25] | 7.00% | [6],[7],[8],[10],[26] |  | 
| Investment, interest rate, paid in cash |  | 12.40% | [1],[2],[3],[5],[25] | 10.10% | [6],[7],[8],[10],[26] |  | 
| Investment, Identifier [Axis]: Viva Railings, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25] | $ 20,747,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25] | $ 20,436,000 |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[25] | 7.10% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25] | 12.40% |  |  |  |  | 
| Investment, Identifier [Axis]: Viva Railings, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[26] |  |  | $ 21,800,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26] | $ 21,364,000 |  |  |  |  | 
| Ending Balance | [26] |  |  | $ 21,364,000 |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[26] |  |  | 7.00% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[26] |  |  | 10.10% |  |  | 
| Investment, Identifier [Axis]: WB Xcel Holdings, LLC - Preferred Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares | [15],[17],[18],[20] |  |  | 333 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 5,687,000 |  |  |  |  | 
| Ending Balance | [18],[20] |  |  | $ 5,687,000 |  |  | 
| Investment, Identifier [Axis]: WB Xcel Holdings, LLC - Preferred Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 333 |  |  |  |  | 
| Net Realized Gain (Loss) for Period |  | $ 0 |  |  |  |  | 
| Amount of Investment Income |  | 0 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 5,687,000 |  |  |  |  | 
| Gross Additions |  | 0 |  |  |  |  | 
| Gross Reductions |  | 0 |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | (5,687,000) |  |  |  |  | 
| Ending Balance |  | 0 |  | 5,687,000 |  |  | 
| Investment, Identifier [Axis]: WB Xcel Holdings, LLC – Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 1,468,000 | [22],[23],[27] | 1,468,000 | [15],[17],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [20] | 1,468,000 |  |  |  |  | 
| Ending Balance |  | 1,468,000 | [27] | 1,468,000 | [20] |  | 
| Line of credit facility, available |  | $ 32,000 | [1],[2],[3],[5],[27] | $ 32,000 | [6],[7],[8],[10],[20] |  | 
| Investment, reference rate and spread |  | 10.50% | [1],[2],[3],[5],[27] | 10.50% | [6],[7],[8],[10],[20] |  | 
| Investment, interest rate, paid in cash |  | 15.80% | [1],[2],[3],[5],[27] | 13.60% | [6],[7],[8],[10],[20] |  | 
| Investment, Identifier [Axis]: WB Xcel Holdings, LLC – Preferred Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares | [22],[23],[27],[28] | 333,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [27],[28] | $ 0 |  |  |  |  | 
| Investment, Identifier [Axis]: WB Xcel Holdings, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[27] | 9,825,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [27] | $ 9,825,000 |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[27] | 10.50% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[27] | 15.80% |  |  |  |  | 
| Investment, Identifier [Axis]: WB Xcel Holdings, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[20] |  |  | $ 9,925,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [20] | $ 9,925,000 |  |  |  |  | 
| Ending Balance | [20] |  |  | $ 9,925,000 |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[20] |  |  | 10.50% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[20] |  |  | 13.60% |  |  | 
| Investment, Identifier [Axis]: WB Xcel Holdings, LLC—Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 1,468,000 |  |  |  |  | 
| Net Realized Gain (Loss) for Period |  | 0 |  |  |  |  | 
| Amount of Investment Income |  | 226,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 1,468,000 |  |  |  |  | 
| Gross Additions |  | 0 |  |  |  |  | 
| Gross Reductions |  | 0 |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 0 |  |  |  |  | 
| Ending Balance |  | 1,468,000 |  | $ 1,468,000 |  |  | 
| Investment, Identifier [Axis]: WB Xcel Holdings, LLC—Term Loan |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount |  | 9,825,000 |  |  |  |  | 
| Net Realized Gain (Loss) for Period |  | 0 |  |  |  |  | 
| Amount of Investment Income |  | 1,514,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance |  | 9,925,000 |  |  |  |  | 
| Gross Additions |  | 0 |  |  |  |  | 
| Gross Reductions |  | (100,000) |  |  |  |  | 
| Net Unrealized Appreciation (Depreciation) |  | 0 |  |  |  |  | 
| Ending Balance |  | $ 9,825,000 |  | $ 9,925,000 |  |  | 
| Investment, Identifier [Axis]: WorkforceQA, LLC – Common Stock |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Shares |  | 532,000 | [22],[23],[27],[28] | 500 | [15],[17],[18],[20] |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [18],[20] | $ 456,000 |  |  |  |  | 
| Ending Balance |  | 359,000 | [27],[28] | $ 456,000 | [18],[20] |  | 
| Investment, Identifier [Axis]: WorkforceQA, LLC – Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25] | 400,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25] | 400,000 |  |  |  |  | 
| Line of credit facility, available | [1],[2],[3],[5],[25] | $ 1,600,000 |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[25] | 6.50% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25] | 11.80% |  |  |  |  | 
| Investment, Identifier [Axis]: WorkforceQA, LLC – Term Debt |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[26],[33],[46] |  |  | 10,000,000 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26],[33],[46] | $ 9,975,000 |  |  |  |  | 
| Ending Balance | [26],[33],[46] |  |  | $ 9,975,000 |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[26],[33],[46] |  |  | 8.50% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[26],[33],[46] |  |  | 11.60% |  |  | 
| Investment, Identifier [Axis]: WorkforceQA, LLC – Term Debt 1 |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25],[47] | 10,000,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25],[47] | $ 9,987,000 |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[25],[47] | 8.40% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25],[47] | 13.70% |  |  |  |  | 
| Investment, Identifier [Axis]: WorkforceQA, LLC – Term Debt 2 |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [22],[23],[25],[47] | $ 1,600,000 |  |  |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Ending Balance | [25],[47] | $ 1,598,000 |  |  |  |  | 
| Investment, reference rate and spread | [1],[2],[3],[5],[25],[47] | 9.30% |  |  |  |  | 
| Investment, interest rate, paid in cash | [1],[2],[3],[5],[25],[47] | 14.60% |  |  |  |  | 
| Investment, Identifier [Axis]: WorkforceQA, LLC– Line of Credit |  |  |  |  |  |  | 
| Investments in and Advances to Affiliates, Activity [Line Items] |  |  |  |  |  |  | 
| Principal amount | [15],[17],[26],[33] |  |  | $ 0 |  |  | 
| Investments in and Advances to Affiliates, at Fair Value [Roll Forward] |  |  |  |  |  |  | 
| Beginning Balance | [26],[33] | $ 0 |  |  |  |  | 
| Ending Balance | [26],[33] |  |  | 0 |  |  | 
| Line of credit facility, available | [6],[7],[8],[10],[26],[33] |  |  | $ 2,000,000 |  |  | 
| Investment, reference rate and spread | [6],[7],[8],[10],[26],[33] |  |  | 6.50% |  |  | 
| Investment, interest rate, paid in cash | [6],[7],[8],[10],[26],[33] |  |  | 9.60% |  |  | 
|  | 
|  |