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Summary of Significant Accounting Policies - Narrative (Details) |  | 3 Months Ended | 6 Months Ended | 11 Months Ended |  |
--- | --- | --- | --- | --- | --- | ---
Mar. 30, 2020 USD ($) $ / shares shares | Jun. 30, 2024 USD ($) numberOfAgreement | Jun. 30, 2023 USD ($) | Jun. 30, 2024 USD ($) numberOfAgreement | Jun. 30, 2023 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2023 USD ($) numberOfAgreement | Feb. 04, 2016 USD ($)
Securities Financing Transaction [Line Items] |  |  |  |  |  |  |  |
Number of collateralized agreements | numberOfAgreement |  | 1 |  | 1 |  |  | 1 |
Securities purchased under collateralized agreements to resell, cost |  | $ 30,000,000 |  | $ 30,000,000 |  |  | $ 30,000,000 |
Securities purchased under agreements to resell |  | 13,500,000 |  | 13,500,000 |  |  | 16,500,000 |
Cash equivalents |  | 0 |  | 0 |  |  | 0 |
PIK interest income |  | 9,031,000 | $ 7,867,000 | 18,685,000 | $ 16,890,000 |  |  |
Non-cash dividend income |  | $ 7,741,000 | 6,736,000 | $ 15,165,000 | 13,237,000 |  |  |
Investments threshold period past due for nonaccrual status |  | 30 days |  | 30 days |  |  |  |
Deferred tax liability |  | $ 63,000 |  | $ 63,000 |  |  | 0 |
Deferred tax asset |  | $ 0 |  | $ 0 |  |  | $ 594,000 |
Dividend reinvestment plan, share price percentage, threshold |  | 110.00% |  | 110.00% |  |  |  |
Investments in Majority-owned Subsidiaries |  |  |  |  |  |  |  |
Securities Financing Transaction [Line Items] |  |  |  |  |  |  |  |
Shares redeemed for a promissory note (in shares) | shares | 105,030 |  |  |  |  |  |  |
Redemption of shares paid-in-kind | $ 11,315,000 |  |  |  |  |  |  |
Interest rate | 7.00% |  |  |  |  |  |  |
Common Stock |  |  |  |  |  |  |  |
Securities Financing Transaction [Line Items] |  |  |  |  |  |  |  |
Stock repurchase program, authorized amount |  |  |  |  |  |  |  | $ 50,000,000
Common stock repurchased |  | $ 0 | $ 0 | $ 0 | $ 0 | $ 2,948,000 |  |
Common Stock | New Mountain Net Lease Corporation |  |  |  |  |  |  |  |
Securities Financing Transaction [Line Items] |  |  |  |  |  |  |  |
Sale of stock, number of shares issued (in shares) | shares | 105,030 |  |  |  |  |  |  |
Sale of stock, price per share (in dollars per share) | $ / shares | $ 107.73 |  |  |  |  |  |  |
Sale of stock, consideration received | $ 11,315,000 |  |  |  |  |  |  |

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