INVESTMENTS - Investment Portfolio Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024
Total
Fair value, beginning of period	$ 2,888,065	$ 2,361,224
New investments	1,513,133	784,076
Investment restructuring	0	(3,705)
Transfers out of Level 3	(23,452)
Transfers into (out of) Level 3, net		(13,068)
Proceeds from sales of investments / return of capital	(60,754)	(75,894)
Loan origination fees received	(23,082)	(16,202)
Principal repayments received	(347,834)	(390,025)
Fair value, end of period	4,021,527	2,670,249
Payment-in-kind interest / dividends
Total
Realized gain (loss)	$ 22,219	$ 18,158
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)	$ 443	$ 487
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)	$ 11,660	$ 10,770
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)	$ 6,454	$ (13,598)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Non-Control / Non-Affiliate investments and Affiliate investments	Non-Control / Non-Affiliate investments and Affiliate investments
Unrealized appreciation (depreciation)
Total
Realized gain (loss)	$ 34,675	$ 8,026
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	1,414,647	737,548
Investment restructuring	424	(12,566)
Transfers out of Level 3	(4,770)
Transfers into (out of) Level 3, net		(4,008)
Proceeds from sales of investments / return of capital	(36,710)	(75,601)
Loan origination fees received	(21,876)	(15,622)
Principal repayments received	(330,440)	(355,629)
Fair value, end of period	3,478,502	2,201,998
Senior debt and 1st lien notes | Payment-in-kind interest / dividends
Total
Realized gain (loss)	$ 7,037	$ 3,663
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)	$ 443	$ 448
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)	$ 11,096	$ 10,115
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)	$ (4,504)	$ (5,196)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Non-Control / Non-Affiliate investments and Affiliate investments	Non-Control / Non-Affiliate investments and Affiliate investments
Senior debt and 1st lien notes | Unrealized appreciation (depreciation)
Total
Realized gain (loss)	$ 40,978	$ 3,213
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	63,219	29,700
Investment restructuring	(424)	8,861
Transfers out of Level 3	0
Transfers into (out of) Level 3, net		(9,060)
Proceeds from sales of investments / return of capital	0	0
Loan origination fees received	(1,206)	(580)
Principal repayments received	(15,518)	(32,967)
Fair value, end of period	161,104	124,624
Subordinated debt and 2nd lien notes | Payment-in-kind interest / dividends
Total
Realized gain (loss)	$ 3,272	$ 2,991
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)	$ 564	$ 655
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)	$ (117)	$ (8,443)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Non-Control / Non-Affiliate investments and Affiliate investments	Non-Control / Non-Affiliate investments and Affiliate investments
Subordinated debt and 2nd lien notes | Unrealized appreciation (depreciation)
Total
Realized gain (loss)	$ 405	$ 3,155
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	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	(1,876)	(1,429)
Fair value, end of period	13,765	15,934
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 and Affiliate investments	Non-Control / Non-Affiliate investments and Affiliate investments
Structured products | Unrealized appreciation (depreciation)
Total
Realized gain (loss)	$ 353	$ 1,658
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	30,267	7,150
Investment restructuring	0	0
Transfers out of Level 3	(9,071)
Transfers into (out of) Level 3, net		0
Proceeds from sales of investments / return of capital	(12,101)	(90)
Loan origination fees received	0	0
Principal repayments received	0	0
Fair value, end of period	363,138	315,467
Equity shares | Payment-in-kind interest / dividends
Total
Realized gain (loss)	$ 11,910	$ 11,504
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)	$ 4,904	$ 41
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Non-Control / Non-Affiliate investments and Affiliate investments	Non-Control / Non-Affiliate investments and Affiliate investments
Equity shares | Unrealized appreciation (depreciation)
Total
Realized gain (loss)	$ (455)	$ (276)
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	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	1,065	2,680
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 and Affiliate investments	Non-Control / Non-Affiliate investments and Affiliate investments
Equity warrants | Unrealized appreciation (depreciation)
Total
Realized gain (loss)	$ (1,748)	$ 205
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	0
Transfers out of Level 3	0
Transfers into (out of) Level 3, net		0
Proceeds from sales of investments / return of capital	(11,943)	(203)
Loan origination fees received	0	0
Principal repayments received	0	0
Fair value, end of period	3,953	9,546
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 and Affiliate investments
Royalty rights | Unrealized appreciation (depreciation)
Total
Realized gain (loss)	$ (4,858)	$ 71
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net unrealized appreciation (depreciation) on investments