SENIOR SECURITIES (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Feb. 12, 2021	Sep. 20, 2017
SBA-guaranteed debentures Fiscal 2014
Notes
Outstanding Exclusive of Treasury Securities	$ 16,250
SBA-guaranteed debentures Fiscal 2015
Notes
Outstanding Exclusive of Treasury Securities	65,000
SBA-guaranteed debentures Fiscal 2016
Notes
Outstanding Exclusive of Treasury Securities	65,000
SBA-guaranteed debentures Fiscal 2017
Notes
Outstanding Exclusive of Treasury Securities	90,000
SBA-guaranteed debentures Fiscal 2018
Notes
Outstanding Exclusive of Treasury Securities	150,000
SBA-guaranteed debentures Fiscal 2019
Notes
Outstanding Exclusive of Treasury Securities	161,000
SBA-guaranteed debentures Fiscal 2020
Notes
Outstanding Exclusive of Treasury Securities	176,500
SBA-guaranteed debentures Fiscal 2021
Notes
Outstanding Exclusive of Treasury Securities	250,000
SBA-guaranteed debentures Fiscal 2022
Notes
Outstanding Exclusive of Treasury Securities	313,600
SBA-guaranteed debentures Fiscal 2023
Notes
Outstanding Exclusive of Treasury Securities	325,000
Original Credit Facility Fiscal 2012
Notes
Outstanding Exclusive of Treasury Securities	$ 38,000
Asset Coverage per Unit	$ 3,090
Original Credit Facility Fiscal 2013
Notes
Outstanding Exclusive of Treasury Securities	$ 110,000
Asset Coverage per Unit	$ 2,470
Original Credit Facility Fiscal 2014
Notes
Outstanding Exclusive of Treasury Securities	$ 106,500
Asset Coverage per Unit	$ 2,320
Original Credit Facility Fiscal 2015
Notes
Outstanding Exclusive of Treasury Securities	$ 109,500
Asset Coverage per Unit	$ 2,220
Original Credit Facility Fiscal 2016
Notes
Outstanding Exclusive of Treasury Securities	$ 116,000
Asset Coverage per Unit	$ 2,210
Credit Facility Fiscal 2017
Notes
Outstanding Exclusive of Treasury Securities	$ 40,750
Asset Coverage per Unit	$ 3,460
Credit Facility Fiscal 2018
Notes
Outstanding Exclusive of Treasury Securities	$ 99,550
Asset Coverage per Unit	$ 2,520
Credit Facility Fiscal 2019
Notes
Outstanding Exclusive of Treasury Securities	$ 161,550
Asset Coverage per Unit	$ 2,286
Credit Facility Fiscal 2020
Notes
Outstanding Exclusive of Treasury Securities	$ 174,000
Asset Coverage per Unit	$ 2,230
Credit Facility Fiscal 2021
Notes
Outstanding Exclusive of Treasury Securities	$ 177,340
Asset Coverage per Unit	$ 2,030
Credit Facility Fiscal 2022
Notes
Outstanding Exclusive of Treasury Securities	$ 199,200
Asset Coverage per Unit	$ 1,920
Credit Facility Fiscal 2023
Notes
Outstanding Exclusive of Treasury Securities	$ 160,086
Asset Coverage per Unit	$ 2,230
4.875% Notes due 202
Notes
Notes interest rate	4.875%
4.875% Notes due 2026, Fiscal 2021
Notes
Outstanding Exclusive of Treasury Securities	$ 100,000
Asset Coverage per Unit	$ 2,030
4.875% Notes due 2026, Fiscal 2022
Notes
Outstanding Exclusive of Treasury Securities	$ 100,000
Asset Coverage per Unit	$ 1,920
4.875% Notes due 2026, Fiscal 2023
Notes
Outstanding Exclusive of Treasury Securities	$ 100,000
Asset Coverage per Unit	$ 2,230
5.75% Notes due 2022
Notes
Notes interest rate	5.75%	5.75%
5.75% Notes due 2022, Fiscal 2017
Notes
Outstanding Exclusive of Treasury Securities	$ 48,875
Asset Coverage per Unit	$ 3,460
Average Market Value per Unit	$ 25.34
5.75% Notes due 2022, Fiscal 2018
Notes
Outstanding Exclusive of Treasury Securities	$ 48,875
Asset Coverage per Unit	$ 2,520
Average Market Value per Unit	$ 25.18
5.75% Notes due 2022, Fiscal 2019
Notes
Outstanding Exclusive of Treasury Securities	$ 48,875
Asset Coverage per Unit	$ 2,286
Average Market Value per Unit	$ 24.43
5.75% Notes due 2022, Fiscal 2020
Notes
Outstanding Exclusive of Treasury Securities	$ 48,875
Asset Coverage per Unit	$ 2,230
Average Market Value per Unit	$ 23.64
6.50% Notes due 2019
Notes
Notes interest rate	6.50%		6.50%
6.50% Notes due 2019, Fiscal 2014
Notes
Outstanding Exclusive of Treasury Securities	$ 25,000
Asset Coverage per Unit	$ 2,320
Average Market Value per Unit	$ 25.41
6.50% Notes due 2019, Fiscal 2015
Notes
Outstanding Exclusive of Treasury Securities	$ 25,000
Asset Coverage per Unit	$ 2,220
Average Market Value per Unit	$ 25.27
6.50% Notes due 2019, Fiscal 2016
Notes
Outstanding Exclusive of Treasury Securities	$ 25,000
Asset Coverage per Unit	$ 2,210
Average Market Value per Unit	$ 25.11
Short-Term Loan, Fiscal 2012
Notes
Outstanding Exclusive of Treasury Securities	$ 45,000
Asset Coverage per Unit	$ 3,090
Short-Term Loan, Fiscal 2013
Notes
Outstanding Exclusive of Treasury Securities	$ 9,000
Asset Coverage per Unit	$ 2,470