INVESTMENTS - Composition of Investments at Fair Value (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Schedule of Investments [Line Items]
Cost	$ 3,826,731		$ 3,813,127
Fair Value	$ 3,788,178		$ 3,791,494
Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	100.00%	100.00%	100.00%
Australia
Schedule of Investments [Line Items]
Cost	$ 8,784		$ 8,798
Fair Value	$ 8,948		$ 8,970
Australia | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	0.20%		0.20%
Canada
Schedule of Investments [Line Items]
Cost	$ 159,651		$ 153,734
Fair Value	$ 161,062		$ 154,953
Canada | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	4.30%		4.10%
United Kingdom
Schedule of Investments [Line Items]
Cost	$ 12,331		$ 12,411
Fair Value	$ 12,140		$ 12,196
United Kingdom | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	0.30%		0.30%
United States
Schedule of Investments [Line Items]
Cost	$ 3,645,965		$ 3,638,184
Fair Value	$ 3,606,028		$ 3,615,375
United States | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	95.20%		95.40%
Aerospace & Defense | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	2.20%	2.20%
Air Freight & Logistics | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	0.40%	0.30%
Automobile Components | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	3.10%	3.00%
Automobiles | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	3.60%	3.60%
Beverages | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	0.10%	0.00%
Biotechnology | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	0.70%	0.70%
Building Products | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	0.40%	0.40%
Chemicals | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	0.50%	0.50%
Commercial Services & Supplies | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	8.60%	9.10%
Construction & Engineering | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	2.10%	2.00%
Consumer Staples Distribution & Retail | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	0.70%	0.70%
Containers & Packaging | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	1.20%	1.20%
Distributors | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	2.00%	2.30%
Diversified Consumer Services | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	4.90%	4.70%
Electrical Equipment | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	0.10%	0.10%
Electronic Equipment, Instruments & Components | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	2.10%	2.10%
Financial Services | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	2.60%	2.50%
Food Products | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	1.90%	2.00%
Ground Transportation | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	0.70%	0.60%
Health Care Equipment & Supplies | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	0.30%	0.60%
Health Care Providers & Services | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	4.90%	5.00%
Health Care Technology | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	1.70%	1.60%
Industrial Conglomerates | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	1.30%	1.20%
Insurance Services | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	12.00%	12.00%
Interactive Media & Services | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	2.60%	2.60%
IT Services | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	8.00%	8.90%
Life Sciences Tools & Services | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	0.30%	0.30%
Machinery | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	1.00%	0.90%
Multi-Utilities | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	0.60%	0.60%
Pharmaceuticals | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	0.30%	0.30%
Professional Services | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	5.30%	5.40%
Real Estate Management & Development | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	4.10%	3.60%
Software | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	19.50%	18.90%
Wireless Telecommunication Services | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	0.20%	0.10%
First Lien Debt
Schedule of Investments [Line Items]
Cost	$ 3,679,424		$ 3,669,886
Fair Value	$ 3,652,320		3,654,538
First Lien Debt | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	96.30%	96.50%
Second Lien Debt
Schedule of Investments [Line Items]
Cost	$ 82,134		78,803
Fair Value	$ 71,190		69,367
Second Lien Debt | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	1.90%	1.80%
Other Debt Investments
Schedule of Investments [Line Items]
Cost	$ 11,008		9,755
Fair Value	$ 9,603		9,198
Other Debt Investments | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	0.30%	0.20%
Equity
Schedule of Investments [Line Items]
Cost	$ 54,165		54,683
Fair Value	$ 55,065		58,391
Equity | Investment Owned at Fair Value | Investment Type Concentration Risk
Schedule of Investments [Line Items]
% of Total Investments at Fair Value	1.50%	1.50%
Equity | Automobile Components
Schedule of Investments [Line Items]
Cost			850
Fair Value			1,463
Equity | Commercial Services & Supplies
Schedule of Investments [Line Items]
Cost			1,907
Fair Value			3,257
Equity | Containers & Packaging
Schedule of Investments [Line Items]
Cost			2,791
Fair Value			1,722
Equity | Distributors
Schedule of Investments [Line Items]
Cost			0
Fair Value			0
Equity | Diversified Consumer Services
Schedule of Investments [Line Items]
Cost			1,303
Fair Value			1,258
Equity | Electrical Equipment
Schedule of Investments [Line Items]
Cost			150
Fair Value			150
Equity | Food Products
Schedule of Investments [Line Items]
Cost			2,013
Fair Value			1,028
Equity | Health Care Providers & Services
Schedule of Investments [Line Items]
Cost			4,955
Fair Value			4,910
Equity | Insurance Services
Schedule of Investments [Line Items]
Cost			4,704
Fair Value			4,727
Equity | IT Services
Schedule of Investments [Line Items]
Cost			13,882
Fair Value			18,845
Equity | Professional Services
Schedule of Investments [Line Items]
Cost			3,492
Fair Value			2,149
Equity | Software
Schedule of Investments [Line Items]
Cost			16,045
Fair Value			$ 16,666