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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 | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2024 | Dec. 31, 2023
Summary of Investment Holdings [Line Items] |  |  |  |
Investments at Fair Value | $ 1,048,071 | [1],[2],[3],[4] | $ 957,906 | [5],[6],[7],[8]
Percentage of Fair Value | 100.00% |  | 100.00% |
Investments at cost | $ 1,025,576 | [1],[2],[3] | $ 936,629 | [5],[6],[7]
Percentage of Cost | 100.00% |  | 100.00% |
United States Midwest |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |
Investments at Fair Value | $ 109,634 |  | $ 112,607 |
Percentage of Fair Value | 10.50% |  | 11.80% |
Investments at cost | $ 75,357 |  | $ 75,436 |
Percentage of Cost | 7.30% |  | 8.10% |
United States Southeast |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |
Investments at Fair Value | $ 320,868 |  | $ 292,408 |
Percentage of Fair Value | 30.60% |  | 30.60% |
Investments at cost | $ 315,567 |  | $ 286,329 |
Percentage of Cost | 30.80% |  | 30.50% |
United States Northeast |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |
Investments at Fair Value | $ 198,218 |  | $ 181,412 |
Percentage of Fair Value | 18.90% |  | 18.90% |
Investments at cost | $ 190,630 |  | $ 176,389 |
Percentage of Cost | 18.60% |  | 18.80% |
United States West |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |
Investments at Fair Value | $ 191,968 |  | $ 172,705 |
Percentage of Fair Value | 18.30% |  | 18.00% |
Investments at cost | $ 210,156 |  | $ 191,545 |
Percentage of Cost | 20.50% |  | 20.50% |
United States Southwest |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |
Investments at Fair Value | $ 214,883 |  | $ 186,274 |
Percentage of Fair Value | 20.50% |  | 19.40% |
Investments at cost | $ 221,396 |  | $ 194,466 |
Percentage of Cost | 21.60% |  | 20.80% |
Canada |  |  |  |
Summary of Investment Holdings [Line Items] |  |  |  |
Investments at Fair Value | $ 12,500 |  | $ 12,500 |
Percentage of Fair Value | 1.20% |  | 1.30% |
Investments at cost | $ 12,470 |  | $ 12,464 |
Percentage of Cost | 1.20% |  | 1.30% |
[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. The Company’s investments are generally classified as “restricted securities”, unless otherwise noted, as such term is defined under Regulation S-X Rule 6-03(f) or Securities Act Rule 144. As of March 31, 2024, the Company held restricted securities with an aggregate fair value of $1,047,818, or 172% of the Company's net assets.
[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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