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Investments - Selected Statement of Operations Information for SLP III and SLP IV (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Investment Company, Nonconsolidated Subsidiary [Line Items] |  |  |
Total investment income | $ 294,630 | $ 270,959 | $ 273,711
Interest and other financing expenses | 92,421 | 73,098 | 78,047
Total expenses | 178,841 | 165,349 | 170,080
Net investment income before income taxes | 120,429 | 118,958 | 117,366
Net realized (losses) gains on investments | 52,703 | (3,864) | (2,802)
Net change in unrealized (depreciation) appreciation of investments | (84,134) | 92,386 | (53,718)
SLP III |  |  |
Investment Company, Nonconsolidated Subsidiary [Line Items] |  |  |
Interest income | 41,382 | 31,240 | 27,476
Other income | 774 | 573 | 576
Total investment income | 42,156 | 31,813 | 28,052
Interest and other financing expenses | 19,274 | 10,624 | 11,872
Other expenses | 863 | 804 | 747
Total expenses | 20,137 | 11,428 | 12,619
Net investment income before income taxes | 22,019 | 20,385 | 15,433
Net realized (losses) gains on investments | (247) | 572 | 262
Net change in unrealized (depreciation) appreciation of investments | (42,366) | 6,360 | (418)
Net (decrease) increase in members' capital | (20,594) | 27,317 | $ 15,277
SLP IV |  |  |
Investment Company, Nonconsolidated Subsidiary [Line Items] |  |  |
Interest income | 31,017 | 14,821 |
Other income | 561 | 234 |
Total investment income | 31,578 | 15,055 |
Interest and other financing expenses | 13,580 | 4,163 |
Other expenses | 757 | 773 |
Total expenses | 14,337 | 4,936 |
Net investment income before income taxes | 17,241 | 10,119 |
Net realized (losses) gains on investments | (164) | 183 |
Net change in unrealized (depreciation) appreciation of investments | (31,018) | 5,033 |
Net (decrease) increase in members' capital | $ (13,941) | $ 15,335 |

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