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Portfolio Company Investments - Schedule of Portfolio Composition by Geographic Region at Fair Value and Cost and as Percentage of Total Investments (Details) - USD ($) $ in Thousands | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2023 | Dec. 31, 2022
Summary of Investment Holdings [Line Items] |  |  |  |
Investments at Fair Value | $ 926,859 | [1],[2],[3],[4] | $ 860,329 | [5],[6],[7],[8]
Percentage of Fair Value | 100.00% |  | 100.00% |
Investments at cost | $ 895,362 | [1],[2],[3] | $ 828,693 | [5],[6],[7]
Percentage of Cost | 100.00% |  | 100.00% |
United States Midwest |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |
Investments at Fair Value | $ 147,123 |  | $ 180,556 |
Percentage of Fair Value | 15.90% |  | 21.00% |
Investments at cost | $ 107,068 |  | $ 132,177 |
Percentage of Cost | 12.00% |  | 16.00% |
United States Southeast |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |
Investments at Fair Value | $ 294,840 |  | $ 265,902 |
Percentage of Fair Value | 31.90% |  | 31.00% |
Investments at cost | $ 281,638 |  | $ 258,373 |
Percentage of Cost | 31.40% |  | 31.10% |
United States Northeast |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |
Investments at Fair Value | $ 152,938 |  | $ 127,427 |
Percentage of Fair Value | 16.50% |  | 14.80% |
Investments at cost | $ 149,427 |  | $ 134,897 |
Percentage of Cost | 16.70% |  | 16.30% |
United States West |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |
Investments at Fair Value | $ 167,020 |  | $ 151,487 |
Percentage of Fair Value | 18.00% |  | 17.60% |
Investments at cost | $ 184,836 |  | $ 161,935 |
Percentage of Cost | 20.60% |  | 19.50% |
United States Southwest |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |
Investments at Fair Value | $ 152,438 |  | $ 122,519 |
Percentage of Fair Value | 16.40% |  | 14.20% |
Investments at cost | $ 159,936 |  | $ 128,873 |
Percentage of Cost | 17.90% |  | 15.60% |
Canada |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |
Investments at Fair Value | $ 12,500 |  | $ 12,438 |
Percentage of Fair Value | 1.30% |  | 1.40% |
Investments at cost | $ 12,457 |  | $ 12,438 |
Percentage of Cost | 1.40% |  | 1.50% |
[1] | (a) See Note 3 to the consolidated financial statements for portfolio composition by geographic location.
[2] | (b) Equity ownership may be held in shares or units of companies related to the portfolio companies.
[3] | (c) All debt investments are income producing, unless otherwise indicated. Equity investments are non-income producing unless otherwise noted.
[4] | (g) Except as otherwise noted, the Company’s investment portfolio is comprised of debt and equity securities of privately held companies for which quoted prices falling within the categories of Level 1 and Level 2 inputs are not available. Therefore, the Company values all of its portfolio investments at fair value, as determined in good faith by the board of directors, using significant unobservable Level 3 inputs.
[5] | (a) See Note 3 to the consolidated financial statements for portfolio composition by geographic location.
[6] | (b) Equity ownership may be held in shares or units of companies related to the portfolio companies.
[7] | (c) All debt investments are income producing, unless otherwise indicated. Equity investments are non-income producing unless otherwise noted.
[8] | (g) Except as otherwise noted, the Company’s investment portfolio is comprised of debt and equity securities of privately held companies for which quoted prices falling within the categories of Level 1 and Level 2 inputs are not available. Therefore, the Company values all of its portfolio investments at fair value, as determined in good faith by the board of directors, using significant unobservable Level 3 inputs.

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