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INVESTMENTS - Schedule of Changes in Level 3 Fair Value Measurements of Investments (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024 | Jun. 30, 2025 | Mar. 31, 2025 | Jun. 30, 2024 | Mar. 31, 2024
New investments, repayments and settlements: |  |  |  |  |  |  |  |  |
Investments, cost | $ 1,037,200 |  | $ 1,037,200 |  |  | $ 939,066 | [1] |  |
PSI Molded |  |  |  |  |  |  |  |  |
New investments, repayments and settlements: |  |  |  |  |  |  |  |  |
Investments, cost |  |  |  |  | $ 10,600 |  |  |  |
Total |  |  |  |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |  |  |  |  |
Beginning balance | 1,125,784 | $ 853,307 | 1,125,784 | $ 853,307 | 1,031,735 | 974,345 |  | $ 899,138 | $ 920,486
New investments, repayments and settlements: |  |  |  |  |  |  |  |  |
Issuances / originations | 71,036 | 19,500 | 133,878 | 20,098 |  |  |  |  |
Settlements / repayments | (1,436) | (25,000) | (5,806) | (28,000) |  |  |  |  |
Sales | 0 | (48,503) | 0 | (48,503) |  |  |  |  |
Transfers | 0 | 0 | 0 | 0 |  |  |  |  |
Ending balance | 1,125,784 | 853,307 | 1,125,784 | 853,307 |  |  |  |  |
Total | Debt and Equity Securities, Realized Gain (Loss) |  |  |  |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |  |  |  |  |
Total gain (loss) | (29,938) | 42,284 | (29,938) | 42,284 |  |  |  |  |
Total | Debt and Equity Securities, Unrealized Gain (Loss) |  |  |  |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |  |  |  |  |
Total gain (loss) | 35,283 | 3,916 | 34,201 | (15,030) |  |  |  |  |
Reversal of previously recorded (appreciation) depreciation upon realization | 19,104 | (38,028) | 19,104 | (38,028) |  |  |  |  |
Secured First Lien Debt |  |  |  |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |  |  |  |  |
Beginning balance | 593,979 | 469,480 | 593,979 | 469,480 | 557,057 | 514,334 |  | 463,219 | 474,856
New investments, repayments and settlements: |  |  |  |  |  |  |  |  |
Issuances / originations | 49,936 | 19,500 | 95,876 | 20,098 |  |  |  |  |
Settlements / repayments | (1,436) | 0 | (5,806) | (3,000) |  |  |  |  |
Sales | 0 | 0 | 0 | 0 |  |  |  |  |
Transfers | 0 | 0 | 0 | 0 |  |  |  |  |
Ending balance | 593,979 | 469,480 | 593,979 | 469,480 |  |  |  |  |
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) | (29,938) | 0 | (29,938) | 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) | (744) | (13,239) | 409 | (22,474) |  |  |  |  |
Reversal of previously recorded (appreciation) depreciation upon realization | 19,104 | 0 | 19,104 | 0 |  |  |  |  |
Secured Second Lien Debt |  |  |  |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |  |  |  |  |
Beginning balance | 90,633 | 111,344 | 90,633 | 111,344 | 93,340 | 103,580 |  | 137,827 | 138,703
New investments, repayments and settlements: |  |  |  |  |  |  |  |  |
Issuances / originations | 0 | 0 | 0 | 0 |  |  |  |  |
Settlements / repayments | 0 | (25,000) | 0 | (25,000) |  |  |  |  |
Sales | 0 | 0 | 0 | 0 |  |  |  |  |
Transfers | 0 | 0 | (10,616) | 0 |  |  |  |  |
Ending balance | 90,633 | 111,344 | 90,633 | 111,344 |  |  |  |  |
Secured Second Lien Debt | PSI Molded |  |  |  |  |  |  |  |  |
New investments, repayments and settlements: |  |  |  |  |  |  |  |  |
Investments, cost | 10,600 |  | 10,600 |  |  |  |  |  |
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) | (2,707) | (1,483) | (2,331) | (2,359) |  |  |  |  |
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 | 365,278 | 228,528 | 365,278 | 228,528 | 325,997 | 302,163 |  | 212,591 | 213,480
New investments, repayments and settlements: |  |  |  |  |  |  |  |  |
Issuances / originations | 21,100 | 0 | 38,002 | 0 |  |  |  |  |
Settlements / repayments | 0 | 0 | 0 | 0 |  |  |  |  |
Sales | 0 | 0 | 0 | 0 |  |  |  |  |
Transfers | 0 | 0 | 10,616 | 0 |  |  |  |  |
Ending balance | 365,278 | 228,528 | 365,278 | 228,528 |  |  |  |  |
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 | 0 | 0 | 0 |  |  |  |  |
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) | 18,181 | 15,937 | 14,497 | 15,048 |  |  |  |  |
Reversal of previously recorded (appreciation) depreciation upon realization | 0 | 0 | 0 | 0 |  |  |  |  |
Common Equity/ Equivalents |  |  |  |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |  |  |  |  |
Beginning balance | 75,894 | 43,955 | 75,894 | 43,955 | $ 55,341 | $ 54,268 |  | $ 85,501 | $ 93,447
New investments, repayments and settlements: |  |  |  |  |  |  |  |  |
Issuances / originations | 0 | 0 | 0 | 0 |  |  |  |  |
Settlements / repayments | 0 | 0 | 0 | 0 |  |  |  |  |
Sales | 0 | (48,503) | 0 | (48,503) |  |  |  |  |
Transfers | 0 | 0 | 0 | 0 |  |  |  |  |
Ending balance | 75,894 | 43,955 | 75,894 | 43,955 |  |  |  |  |
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 | 42,284 | 0 | 42,284 |  |  |  |  |
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) | 20,553 | 2,701 | 21,626 | (5,245) |  |  |  |  |
Reversal of previously recorded (appreciation) depreciation upon realization | $ 0 | $ (38,028) | $ 0 | $ (38,028) |  |  |  |  |
[1] | Cumulative gross unrealized appreciation for federal income tax purposes is $183.3 million; cumulative gross unrealized depreciation for federal income tax purposes is $144.9 million. Cumulative net unrealized appreciation is $38.5 million, based on a tax cost of $940.9 million.

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