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INVESTMENTS - Schedule of Changes in Level 3 Fair Value Measurements of Investments (Details) - USD ($) $ in Thousands | 1 Months Ended | 3 Months Ended | 9 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | ---
Sep. 30, 2024 | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2024 | Dec. 31, 2023 | Mar. 31, 2024 | Sep. 30, 2023 | Mar. 31, 2023
New investments, repayments and settlements: |  |  |  |  |  |  |  |  |
Cost |  | $ 1,021,741 |  | $ 1,021,741 |  | $ 854,290 | [1] |  |
Fair Value |  | 1,072,230 |  | 1,072,230 |  | 920,504 | [1] |  |
Old World Christmas, Inc. |  |  |  |  |  |  |  |  |
New investments, repayments and settlements: |  |  |  |  |  |  |  |  |
Realized gain (loss) on preferred equity |  |  |  |  | $ 300 |  |  |  |
SFEG Holdings, Inc |  |  |  |  |  |  |  |  |
New investments, repayments and settlements: |  |  |  |  |  |  |  |  |
Cost |  |  | $ 4,800 |  | 4,800 |  |  |  |
Fair Value |  |  | 8,600 |  | 8,600 |  |  |  |
Total |  |  |  |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |  |  |  |  |
Beginning balance | $ 853,307 | 1,067,230 | 902,786 | 1,067,230 | 902,786 | 920,486 |  | $ 915,614 | $ 753,516
New investments, repayments and settlements: |  |  |  |  |  |  |  |  |
Issuances / originations |  | 182,094 | 68,200 | 202,192 | 182,988 |  |  |  |
Settlements / repayments |  | (5,500) | (27,500) | (33,500) | (27,500) |  |  |  |
Sales |  | 0 | (50,453) | (48,503) | (52,228) |  |  |  |
Transfers |  | 0 | 0 | 0 | 0 |  |  |  |
Ending balance | 853,307 | 1,067,230 | 902,786 | 1,067,230 | 902,786 |  |  |  |
Total | Debt and Equity Securities, Realized Gain (Loss) |  |  |  |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |  |  |  |  |
Total gain (loss) |  | 0 | 43,459 | 42,284 | 44,614 |  |  |  |
Total | Debt and Equity Securities, Unrealized Gain (Loss) |  |  |  |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |  |  |  |  |
Total gain (loss) |  | 37,329 | (2,968) | 22,299 | 45,055 |  |  |  |
Reversal of previously recorded (appreciation) depreciation upon realization |  | 0 | (43,566) | (38,028) | (43,659) |  |  |  |
Secured First Lien Debt |  |  |  |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |  |  |  |  |
Beginning balance | 469,480 | 599,911 | 476,126 | 599,911 | 476,126 | 474,856 |  | 508,504 | 437,517
New investments, repayments and settlements: |  |  |  |  |  |  |  |  |
Issuances / originations |  | 135,477 | 3,500 | 155,575 | 73,600 |  |  |  |
Settlements / repayments |  | (5,500) | (27,500) | (8,500) | (27,500) |  |  |  |
Sales |  | 0 | 0 | 0 | 0 |  |  |  |
Transfers |  | 0 | 0 | 0 | 0 |  |  |  |
Ending balance | 469,480 | 599,911 | 476,126 | 599,911 | 476,126 |  |  |  |
Secured First Lien Debt | Debt and Equity Securities, Realized Gain (Loss) |  |  |  |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |  |  |  |  |
Total gain (loss) |  | 0 | 0 | 0 | 0 |  |  |  |
Secured First Lien Debt | Debt and Equity Securities, Unrealized Gain (Loss) |  |  |  |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |  |  |  |  |
Total gain (loss) |  | 454 | (7,040) | (22,020) | (6,153) |  |  |  |
Reversal of previously recorded (appreciation) depreciation upon realization |  | 0 | (1,338) | 0 | (1,338) |  |  |  |
Secured Second Lien Debt |  |  |  |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |  |  |  |  |
Beginning balance | 111,344 | 108,743 | 137,480 | 108,743 | 137,480 | 138,703 |  | 102,747 | 75,734
New investments, repayments and settlements: |  |  |  |  |  |  |  |  |
Issuances / originations |  | 0 | 39,000 | 0 | 64,000 |  |  |  |
Settlements / repayments |  | 0 | 0 | (25,000) | 0 |  |  |  |
Sales |  | 0 | 0 | 0 | 0 |  |  |  |
Transfers |  | 0 | 0 | 0 | 0 |  |  |  |
Ending balance | 111,344 | 108,743 | 137,480 | 108,743 | 137,480 |  |  |  |
Secured Second Lien Debt | Debt and Equity Securities, Realized Gain (Loss) |  |  |  |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |  |  |  |  |
Total gain (loss) |  | 0 | 0 | 0 | 0 |  |  |  |
Secured Second Lien Debt | Debt and Equity Securities, Unrealized Gain (Loss) |  |  |  |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |  |  |  |  |
Total gain (loss) |  | (2,601) | (4,267) | (4,960) | (2,254) |  |  |  |
Reversal of previously recorded (appreciation) depreciation upon realization |  | 0 | 0 | 0 | 0 |  |  |  |
Preferred Equity |  |  |  |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |  |  |  |  |
Beginning balance | 228,528 | 308,226 | 214,664 | 308,226 | 214,664 | 213,480 |  | 267,596 | 222,585
New investments, repayments and settlements: |  |  |  |  |  |  |  |  |
Issuances / originations |  | 46,617 | 0 | 46,617 | 14,688 |  |  |  |
Settlements / repayments |  | 0 | 0 | 0 | 0 |  |  |  |
Sales |  | 0 | (50,453) | 0 | (50,726) |  |  |  |
Transfers |  | 0 | (8,621) | 0 | (8,621) |  |  |  |
Ending balance | 228,528 | 308,226 | 214,664 | 308,226 | 214,664 |  |  |  |
Preferred Equity | Debt and Equity Securities, Realized Gain (Loss) |  |  |  |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |  |  |  |  |
Total gain (loss) |  | 0 | 43,459 | 0 | 43,732 |  |  |  |
Preferred Equity | Debt and Equity Securities, Unrealized Gain (Loss) |  |  |  |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |  |  |  |  |
Total gain (loss) |  | 33,081 | 4,911 | 48,129 | 35,234 |  |  |  |
Reversal of previously recorded (appreciation) depreciation upon realization |  | 0 | (42,228) | 0 | (42,228) |  |  |  |
Common Equity/ Equivalents |  |  |  |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |  |  |  |  |
Beginning balance | 43,955 | 50,350 | 74,516 | 50,350 | 74,516 | $ 93,447 |  | $ 36,767 | $ 17,680
New investments, repayments and settlements: |  |  |  |  |  |  |  |  |
Issuances / originations |  | 0 | 25,700 | 0 | 30,700 |  |  |  |
Settlements / repayments |  | 0 | 0 | 0 | 0 |  |  |  |
Sales |  | 0 | 0 | (48,503) | (1,502) |  |  |  |
Transfers |  | 0 | 8,621 | 0 | 8,621 |  |  |  |
Ending balance | $ 43,955 | 50,350 | 74,516 | 50,350 | 74,516 |  |  |  |
Common Equity/ Equivalents | Debt and Equity Securities, Realized Gain (Loss) |  |  |  |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |  |  |  |  |
Total gain (loss) |  | 0 | 0 | 42,284 | 882 |  |  |  |
Common Equity/ Equivalents | Debt and Equity Securities, Unrealized Gain (Loss) |  |  |  |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |  |  |  |  |
Total gain (loss) |  | 6,395 | 3,428 | 1,150 | 18,228 |  |  |  |
Reversal of previously recorded (appreciation) depreciation upon realization |  | $ 0 | $ 0 | $ (38,028) | $ (93) |  |  |  |
[1] | Cumulative gross unrealized appreciation for federal income tax purposes is $180.5 million; cumulative gross unrealized depreciation for federal income tax purposes is $115.8 million. Cumulative net unrealized appreciation is $64.7 million, based on a tax cost of $855.8 million.

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