INVESTMENTS - Investment Portfolio Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024
Total
Fair value, beginning of period	$ 2,888,065	$ 2,361,224
New investments	918,348	528,734
Investment restructuring		(3,705)
Transfers out of Level 3	(9,611)
Transfers into (out of) Level 3, net		(100)
Proceeds from sales of investments / return of capital	(50,353)	(75,601)
Loan origination fees received	(17,059)	(11,843)
Principal repayments received	(162,530)	(287,880)
Fair value, end of period	3,642,444	2,510,007
Payment-in-kind interest / dividends
Total
Realized gain (loss)	$ 14,623	$ 11,116
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Total payment-in-kind interest income	Total payment-in-kind interest income
Accretion of loan premium / discount
Total
Realized gain (loss)	$ 277	$ 343
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Interest and other financing fees	Interest and other financing fees
Accretion of deferred loan origination revenue
Total
Realized gain (loss)	$ 7,205	$ 7,300
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Interest and other financing fees	Interest and other financing fees
Realized gain (loss)
Total
Realized gain (loss)	$ 5,661	$ (11,713)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Non-Control / Non-Affiliate investments	Non-Control / Non-Affiliate investments
Unrealized appreciation (depreciation)
Total
Realized gain (loss)	$ 47,818	$ (7,868)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net unrealized appreciation (depreciation) on investments	Net unrealized appreciation (depreciation) on investments
Senior debt and 1st lien notes
Total
Fair value, beginning of period	$ 2,402,177	$ 1,915,633
New investments	844,116	486,743
Investment restructuring		(12,566)
Transfers out of Level 3	0
Transfers into (out of) Level 3, net		(100)
Proceeds from sales of investments / return of capital	(34,766)	(75,601)
Loan origination fees received	(15,904)	(11,263)
Principal repayments received	(148,302)	(257,304)
Fair value, end of period	3,103,494	2,041,290
Senior debt and 1st lien notes | Payment-in-kind interest / dividends
Total
Realized gain (loss)	$ 4,506	$ 1,614
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Total payment-in-kind interest income	Total payment-in-kind interest income
Senior debt and 1st lien notes | Accretion of loan premium / discount
Total
Realized gain (loss)	$ 277	$ 304
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Interest and other financing fees	Interest and other financing fees
Senior debt and 1st lien notes | Accretion of deferred loan origination revenue
Total
Realized gain (loss)	$ 6,799	$ 6,785
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Interest and other financing fees	Interest and other financing fees
Senior debt and 1st lien notes | Realized gain (loss)
Total
Realized gain (loss)	$ (2,745)	$ (3,334)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Non-Control / Non-Affiliate investments	Non-Control / Non-Affiliate investments
Senior debt and 1st lien notes | Unrealized appreciation (depreciation)
Total
Realized gain (loss)	$ 47,336	$ (9,621)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net unrealized appreciation (depreciation) on investments	Net unrealized appreciation (depreciation) on investments
Subordinated debt and 2nd lien notes
Total
Fair value, beginning of period	$ 110,909	$ 130,273
New investments	48,767	27,873
Investment restructuring		8,861
Transfers out of Level 3	0
Transfers into (out of) Level 3, net		0
Proceeds from sales of investments / return of capital	0	0
Loan origination fees received	(1,155)	(580)
Principal repayments received	(12,895)	(29,862)
Fair value, end of period	148,432	131,644
Subordinated debt and 2nd lien notes | Payment-in-kind interest / dividends
Total
Realized gain (loss)	$ 1,787	$ 1,440
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Total payment-in-kind interest income	Total payment-in-kind interest income
Subordinated debt and 2nd lien notes | Accretion of loan premium / discount
Total
Realized gain (loss)	$ 0	$ 39
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Interest and other financing fees	Interest and other financing fees
Subordinated debt and 2nd lien notes | Accretion of deferred loan origination revenue
Total
Realized gain (loss)	$ 406	$ 515
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Interest and other financing fees	Interest and other financing fees
Subordinated debt and 2nd lien notes | Realized gain (loss)
Total
Realized gain (loss)	$ (149)	$ (8,379)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Non-Control / Non-Affiliate investments	Non-Control / Non-Affiliate investments
Subordinated debt and 2nd lien notes | Unrealized appreciation (depreciation)
Total
Realized gain (loss)	$ 762	$ 1,464
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net unrealized appreciation (depreciation) on investments	Net unrealized appreciation (depreciation) on investments
Structured products
Total
Fair value, beginning of period	$ 19,899	$ 15,705
New investments	5,000	0
Investment restructuring		0
Transfers out of Level 3	(9,611)
Transfers into (out of) Level 3, net		0
Proceeds from sales of investments / return of capital	0	0
Loan origination fees received	0	0
Principal repayments received	(1,333)	(714)
Fair value, end of period	14,384	16,718
Structured products | Payment-in-kind interest / dividends
Total
Realized gain (loss)	$ 0	$ 0
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Total payment-in-kind interest income	Total payment-in-kind interest income
Structured products | Accretion of loan premium / discount
Total
Realized gain (loss)	$ 0	$ 0
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Interest and other financing fees	Interest and other financing fees
Structured products | Accretion of deferred loan origination revenue
Total
Realized gain (loss)	$ 0	$ 0
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Interest and other financing fees	Interest and other financing fees
Structured products | Realized gain (loss)
Total
Realized gain (loss)	$ 0	$ 0
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Non-Control / Non-Affiliate investments	Non-Control / Non-Affiliate investments
Structured products | Unrealized appreciation (depreciation)
Total
Realized gain (loss)	$ 429	$ 1,727
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net unrealized appreciation (depreciation) on investments	Net unrealized appreciation (depreciation) on investments
Equity shares
Total
Fair value, beginning of period	$ 337,684	$ 297,138
New investments	20,465	4,440
Investment restructuring		0
Transfers out of Level 3	0
Transfers into (out of) Level 3, net		0
Proceeds from sales of investments / return of capital	(3,701)	0
Loan origination fees received	0	0
Principal repayments received	0	0
Fair value, end of period	371,196	307,969
Equity shares | Payment-in-kind interest / dividends
Total
Realized gain (loss)	$ 8,330	$ 8,062
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Total payment-in-kind interest income	Total payment-in-kind interest income
Equity shares | Accretion of loan premium / discount
Total
Realized gain (loss)	$ 0	$ 0
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Interest and other financing fees	Interest and other financing fees
Equity shares | Accretion of deferred loan origination revenue
Total
Realized gain (loss)	$ 0	$ 0
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Interest and other financing fees	Interest and other financing fees
Equity shares | Realized gain (loss)
Total
Realized gain (loss)	$ 2,384	$ 0
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Non-Control / Non-Affiliate investments	Non-Control / Non-Affiliate investments
Equity shares | Unrealized appreciation (depreciation)
Total
Realized gain (loss)	$ 6,034	$ (1,671)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net unrealized appreciation (depreciation) on investments	Net unrealized appreciation (depreciation) on investments
Equity warrants
Total
Fair value, beginning of period	$ 2,813	$ 2,475
New investments	0	0
Investment restructuring		0
Transfers out of Level 3	0
Transfers into (out of) Level 3, net		0
Proceeds from sales of investments / return of capital	0	0
Loan origination fees received	0	0
Principal repayments received	0	0
Fair value, end of period	1,084	2,708
Equity warrants | Payment-in-kind interest / dividends
Total
Realized gain (loss)	$ 0	$ 0
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Total payment-in-kind interest income	Total payment-in-kind interest income
Equity warrants | Accretion of loan premium / discount
Total
Realized gain (loss)	$ 0	$ 0
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Interest and other financing fees	Interest and other financing fees
Equity warrants | Accretion of deferred loan origination revenue
Total
Realized gain (loss)	$ 0	$ 0
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Interest and other financing fees	Interest and other financing fees
Equity warrants | Realized gain (loss)
Total
Realized gain (loss)	$ 0	$ 0
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Non-Control / Non-Affiliate investments	Non-Control / Non-Affiliate investments
Equity warrants | Unrealized appreciation (depreciation)
Total
Realized gain (loss)	$ (1,729)	$ 233
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net unrealized appreciation (depreciation) on investments	Net unrealized appreciation (depreciation) on investments
Royalty rights
Total
Fair value, beginning of period	$ 14,583	$ 0
New investments	0	9,678
Investment restructuring		0
Transfers out of Level 3	0
Transfers into (out of) Level 3, net		0
Proceeds from sales of investments / return of capital	(11,886)	0
Loan origination fees received	0	0
Principal repayments received	0	0
Fair value, end of period	3,854	9,678
Royalty rights | Payment-in-kind interest / dividends
Total
Realized gain (loss)	$ 0	0
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Total payment-in-kind interest income
Royalty rights | Accretion of loan premium / discount
Total
Realized gain (loss)	$ 0	0
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Interest and other financing fees
Royalty rights | Accretion of deferred loan origination revenue
Total
Realized gain (loss)	$ 0	0
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Interest and other financing fees
Royalty rights | Realized gain (loss)
Total
Realized gain (loss)	$ 6,171	0
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Non-Control / Non-Affiliate investments
Royalty rights | Unrealized appreciation (depreciation)
Total
Realized gain (loss)	$ (5,014)	$ 0
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net unrealized appreciation (depreciation) on investments