INVESTMENTS - Investment Portfolio Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Total
Fair value, beginning of period	$ 2,888,065	$ 2,361,224
New investments	397,083	276,060
Investment restructuring		(12,566)
Proceeds from sales of investments / return of capital	(29,109)	(40,481)
Loan origination fees received	(9,512)	(6,096)
Principal repayments received	(52,245)	(120,474)
Fair value, end of period	3,228,587	2,463,117
Payment-in-kind interest / dividends
Total
Realized gain (loss)	$ 6,476	$ 4,576
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)	$ 136	$ 186
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)	$ 3,268	$ 3,149
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)	$ (465)	$ (3,897)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net realized gains (losses) on investments	Net realized gains (losses) on investments
Unrealized appreciation (depreciation)
Total
Realized gain (loss)	$ 24,890	$ 1,436
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	380,147	250,445
Investment restructuring		(12,566)
Proceeds from sales of investments / return of capital	(27,968)	(40,481)
Loan origination fees received	(9,510)	(5,533)
Principal repayments received	(44,957)	(109,084)
Fair value, end of period	2,721,811	1,999,007
Senior debt and 1st lien notes | Payment-in-kind interest / dividends
Total
Realized gain (loss)	$ 2,109	$ 568
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)	$ 136	$ 186
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)	$ 3,059	$ 3,014
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)	$ (586)	$ (3,897)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net realized gains (losses) on investments	Net realized gains (losses) on investments
Senior debt and 1st lien notes | Unrealized appreciation (depreciation)
Total
Realized gain (loss)	$ 17,204	$ 722
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	1,590	21,836
Investment restructuring		0
Proceeds from sales of investments / return of capital	0	0
Loan origination fees received	(2)	(563)
Principal repayments received	(6,574)	(10,676)
Fair value, end of period	107,615	140,424
Subordinated debt and 2nd lien notes | Payment-in-kind interest / dividends
Total
Realized gain (loss)	$ 1,054	$ 789
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	$ 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
Subordinated debt and 2nd lien notes | Accretion of deferred loan origination revenue
Total
Realized gain (loss)	$ 209	$ 135
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)	$ (150)	$ 0
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net realized gains (losses) on investments	Net realized gains (losses) on investments
Subordinated debt and 2nd lien notes | Unrealized appreciation (depreciation)
Total
Realized gain (loss)	$ 579	$ (1,370)
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
Proceeds from sales of investments / return of capital	0	0
Loan origination fees received	0	0
Principal repayments received	(714)	(714)
Fair value, end of period	24,595	16,603
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]	Net realized gains (losses) on investments	Net realized gains (losses) on investments
Structured products | Unrealized appreciation (depreciation)
Total
Realized gain (loss)	$ 410	$ 1,612
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	10,346	3,779
Investment restructuring		0
Proceeds from sales of investments / return of capital	(933)	0
Loan origination fees received	0	0
Principal repayments received	0	0
Fair value, end of period	355,740	304,490
Equity shares | Payment-in-kind interest / dividends
Total
Realized gain (loss)	$ 3,313	$ 3,219
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)	$ 271	$ 0
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net realized gains (losses) on investments	Net realized gains (losses) on investments
Equity shares | Unrealized appreciation (depreciation)
Total
Realized gain (loss)	$ 5,059	$ 354
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
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	2,880	2,593
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]	Net realized gains (losses) on investments	Net realized gains (losses) on investments
Equity warrants | Unrealized appreciation (depreciation)
Total
Realized gain (loss)	$ 67	$ 118
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
New investments	0
Proceeds from sales of investments / return of capital	(208)
Loan origination fees received	0
Principal repayments received	0
Fair value, end of period	15,946
Royalty rights | Payment-in-kind interest / dividends
Total
Realized gain (loss)	$ 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
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
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)	$ 0
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net realized gains (losses) on investments
Royalty rights | Unrealized appreciation (depreciation)
Total
Realized gain (loss)	$ 1,571
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net unrealized appreciation (depreciation) on investments