FINANCIAL HIGHLIGHTS - Financial Highlights, Additional Information (Details) - $ / shares	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Investment Company, Financial Highlights [Line Items]
Additional dividends declared (in dollars per share)			$ 0.12			$ 0.08				$ 0.05
Per share market value at end of period (in dollars per share)	$ 21.89	$ 20.03	18.47	$ 21.19	$ 16.89	18.65	$ 15.58	$ 15.72	$ 16.49	14.25	$ 15.61
Total distributions to stockholders (in dollars per share)	$ 1.92	$ 1.92	$ 1.87	$ 1.62	$ 1.60	$ 1.68	$ 1.54	$ 1.52	$ 1.52	$ 1.57
Ratio of operating expenses to average net assets	12.26%	12.78%	10.19%	13.05%	10.27%	9.92%	8.63%	9.45%	9.59%	9.51%
Base management fee
Investment Company, Financial Highlights [Line Items]
Ratio of operating expenses to average net assets	3.03%	3.11%	3.27%	3.14%	3.10%	2.78%	2.49%	2.57%	2.64%	2.55%
Income based fee and capital gains incentive fee, net of the fee waiver
Investment Company, Financial Highlights [Line Items]
Ratio of operating expenses to average net assets	3.08%	3.66%	1.61%	4.80%	1.80%	2.23%	2.24%	2.18%	2.29%	2.31%
Income based fee and capital gains incentive fee, excluding the fee waiver
Investment Company, Financial Highlights [Line Items]
Ratio of operating expenses to average net assets	3.08%	3.66%	1.61%	4.80%	1.80%	2.64%	2.79%	2.32%	2.29%	2.31%
Interest and credit facility fees
Investment Company, Financial Highlights [Line Items]
Ratio of operating expenses to average net assets	5.79%	5.60%	4.89%	4.61%	4.54%	3.94%	3.33%	3.37%	3.58%	4.32%
Other operating expenses
Investment Company, Financial Highlights [Line Items]
Ratio of operating expenses to average net assets	0.36%	0.41%	0.42%	0.50%	0.83%	0.97%	0.57%	1.33%	1.08%	0.33%