INVESTMENTS - Composition of Investment Portfolio At Cost And Fair Value (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024		Dec. 31, 2023
Schedule of Investments [Line Items]
Cost	$ 1,359,869		$ 1,352,116
Fair Value	$ 1,363,048		$ 1,349,121
Percentage of Total Net Assets	203.40%	[1]	206.90%	[2]
Banff Partners LP
Schedule of Investments [Line Items]
Cost	$ 150,821		$ 151,907
Fair Value	143,697		146,477
Thompson Rivers LLC
Schedule of Investments [Line Items]
Cost	328,095		386,657
Fair Value	$ 307,685		$ 366,731
Investment Owned, At Cost | Investment Type Concentration Risk
Schedule of Investments [Line Items]
Percentage of Total Portfolio	100.00%		100.00%
Investment Owned, At Cost | Investment Type Concentration Risk | Banff Partners LP
Schedule of Investments [Line Items]
Percentage of Total Portfolio	100.00%		100.00%
Investment Owned, At Cost | Investment Type Concentration Risk | Thompson Rivers LLC
Schedule of Investments [Line Items]
Percentage of Total Portfolio	100.00%		100.00%
Investment Owned, At Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
Percentage of Total Portfolio	100.00%		100.00%
Investment Owned, At Fair Value | Investment Type Concentration Risk | Banff Partners LP
Schedule of Investments [Line Items]
Percentage of Total Portfolio	100.00%		100.00%
Investment Owned, At Fair Value | Investment Type Concentration Risk | Thompson Rivers LLC
Schedule of Investments [Line Items]
Percentage of Total Portfolio	100.00%		100.00%
Senior debt and 1st lien notes
Schedule of Investments [Line Items]
Cost	$ 996,015		$ 1,000,294
Fair Value	$ 982,334		$ 985,158
Percentage of Total Net Assets	147.00%		151.00%
Senior debt and 1st lien notes | Banff Partners LP
Schedule of Investments [Line Items]
Cost	$ 146,901		$ 147,990
Fair Value	$ 139,697		$ 142,490
Senior debt and 1st lien notes | Investment Owned, At Cost | Investment Type Concentration Risk
Schedule of Investments [Line Items]
Percentage of Total Portfolio	73.00%		74.00%
Senior debt and 1st lien notes | Investment Owned, At Cost | Investment Type Concentration Risk | Banff Partners LP
Schedule of Investments [Line Items]
Percentage of Total Portfolio	97.00%		97.00%
Senior debt and 1st lien notes | Investment Owned, At Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
Percentage of Total Portfolio	72.00%		73.00%
Senior debt and 1st lien notes | Investment Owned, At Fair Value | Investment Type Concentration Risk | Banff Partners LP
Schedule of Investments [Line Items]
Percentage of Total Portfolio	97.00%		97.00%
Subordinated debt and 2nd lien notes
Schedule of Investments [Line Items]
Cost	$ 108,605		$ 108,487
Fair Value	$ 107,913		$ 106,894
Percentage of Total Net Assets	16.00%		16.00%
Subordinated debt and 2nd lien notes | Banff Partners LP
Schedule of Investments [Line Items]
Cost	$ 3,920		$ 3,917
Fair Value	$ 4,000		$ 3,987
Subordinated debt and 2nd lien notes | Investment Owned, At Cost | Investment Type Concentration Risk
Schedule of Investments [Line Items]
Percentage of Total Portfolio	8.00%		8.00%
Subordinated debt and 2nd lien notes | Investment Owned, At Cost | Investment Type Concentration Risk | Banff Partners LP
Schedule of Investments [Line Items]
Percentage of Total Portfolio	3.00%		3.00%
Subordinated debt and 2nd lien notes | Investment Owned, At Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
Percentage of Total Portfolio	8.00%		8.00%
Subordinated debt and 2nd lien notes | Investment Owned, At Fair Value | Investment Type Concentration Risk | Banff Partners LP
Schedule of Investments [Line Items]
Percentage of Total Portfolio	3.00%		3.00%
Structured products
Schedule of Investments [Line Items]
Cost	$ 28,657		$ 29,479
Fair Value	$ 27,744		$ 26,173
Percentage of Total Net Assets	4.00%		4.00%
Structured products | Investment Owned, At Cost | Investment Type Concentration Risk
Schedule of Investments [Line Items]
Percentage of Total Portfolio	2.00%		2.00%
Structured products | Investment Owned, At Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
Percentage of Total Portfolio	2.00%		2.00%
Equity shares
Schedule of Investments [Line Items]
Cost	$ 176,427		$ 162,731
Fair Value	$ 207,185		$ 192,641
Percentage of Total Net Assets	31.00%		30.00%
Equity shares | Investment Owned, At Cost | Investment Type Concentration Risk
Schedule of Investments [Line Items]
Percentage of Total Portfolio	13.00%		12.00%
Equity shares | Investment Owned, At Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
Percentage of Total Portfolio	15.00%		14.00%
Equity warrants
Schedule of Investments [Line Items]
Cost	$ 33		$ 2
Fair Value	$ 1,147		$ 1,043
Percentage of Total Net Assets	0.00%		0.00%
Equity warrants | Investment Owned, At Cost | Investment Type Concentration Risk
Schedule of Investments [Line Items]
Percentage of Total Portfolio	0.00%		0.00%
Equity warrants | Investment Owned, At Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
Percentage of Total Portfolio	0.00%		0.00%
Investments in joint ventures
Schedule of Investments [Line Items]
Cost	$ 50,132		$ 51,123
Fair Value	$ 36,725		$ 37,212
Percentage of Total Net Assets	5.00%		6.00%
Investments in joint ventures | Investment Owned, At Cost | Investment Type Concentration Risk
Schedule of Investments [Line Items]
Percentage of Total Portfolio	4.00%		4.00%
Investments in joint ventures | Investment Owned, At Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
Percentage of Total Portfolio	3.00%		3.00%
Federal Housing Administration (“FHA”) loans | Thompson Rivers LLC
Schedule of Investments [Line Items]
Cost	$ 306,491		$ 360,847
Fair Value	$ 287,390		$ 342,240
Federal Housing Administration (“FHA”) loans | Investment Owned, At Cost | Investment Type Concentration Risk | Thompson Rivers LLC
Schedule of Investments [Line Items]
Percentage of Total Portfolio	93.00%		93.00%
Federal Housing Administration (“FHA”) loans | Investment Owned, At Fair Value | Investment Type Concentration Risk | Thompson Rivers LLC
Schedule of Investments [Line Items]
Percentage of Total Portfolio	93.00%		93.00%
Veterans Affairs (“VA”) loans | Thompson Rivers LLC
Schedule of Investments [Line Items]
Cost	$ 21,604		$ 25,810
Fair Value	$ 20,295		$ 24,491
Veterans Affairs (“VA”) loans | Investment Owned, At Cost | Investment Type Concentration Risk | Thompson Rivers LLC
Schedule of Investments [Line Items]
Percentage of Total Portfolio	7.00%		7.00%
Veterans Affairs (“VA”) loans | Investment Owned, At Fair Value | Investment Type Concentration Risk | Thompson Rivers LLC
Schedule of Investments [Line Items]
Percentage of Total Portfolio	7.00%		7.00%

[1] Fair value as a percentage of net assets.

[2] Fair value as a percentage of net assets.