SUMMARY OF PER SHARE INFORMATION (Details) - $ / shares	12 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Per Share Data:
Investment income (in usd per share)	$ 4.25	$ 4.37	$ 3.97	$ 3.60	$ 3.57	$ 3.45	$ 3.10	$ 2.18	$ 1.48
Operating expenses (in usd per share)	(1.74)	(1.65)	(1.67)	(1.70)	(1.78)	(1.76)	(1.62)	(1.16)	(0.87)
Income taxes (in usd per share)	(0.05)	(0.02)	(0.01)	(0.03)	(0.13)	(0.12)	(0.06)	(0.01)	(0.11)
Net investment income (in usd per share)	2.46	2.70	2.29	1.87	1.66	1.57	1.42	1.01	0.50
Net realized (loss) gain, net of tax (in usd per share)	(1.03)	(0.98)	(0.57)	0.26	(0.45)	2.35	1.24	0.10	0.50
Net unrealized (depreciation) appreciation on investments, net of tax (in usd per share)	0.05	0.34	(0.62)	0.50	1.51	(5.16)	(0.68)	1.34	0.49
Realized loss on extinguishment of debt (in usd per share)	(0.01)	(0.01)	0	(0.75)	(0.05)	0	0	0	0
Total increase from investment operations (in usd per share)	1.47	2.05	1.10	1.88	2.67	(1.24)	1.98	2.45	1.49
Accretive effect of share issuances and repurchases (in usd per share)	0.94	0.86	0.50	1.45	0.30	0.45	0.06	(0.04)	0
Dividends to shareholders (in usd per share)	(2.54)	(2.47)	(2.28)	(2.52)	(2.05)	(2.75)	(2.27)	(0.99)	(0.79)
Spin-off Compensation Plan Distribution, net of tax (in usd per share)	0	0	0	0	0	0	0	(0.03)	(0.08)
Issuance of restricted stock (in usd per share)	(0.10)	(0.13)	(0.14)	(0.10)	(0.16)	(0.06)	(0.23)	(0.18)	(0.15)
Common stock withheld for payroll taxes upon vesting of restricted stock (in usd per share)	(0.10)	(0.05)	(0.01)	(0.03)	0	0	(0.01)	(0.01)	0
Exercise of employee stock options (in usd per share)	0	0	0	0	0	0	(0.12)	0.01	(0.09)
Share based compensation expense (in usd per share)	0.13	0.10	0.10	0.14	0.14	0.16	0.13	0.11	0.08
Change in restoration plan (in usd per share)	0	0	0.06	0.01	0	(0.01)	(0.01)	(0.05)	0
Repurchase of common stock (in usd per share)	0	0	0	0	0	0.15	0	0	0
Other (in usd per share)	0.13	0.04	0.18	0.02	(0.02)	(0.19)	0.01	0.01	0
(Decrease) increase in net asset value (in usd per share)	(0.07)	0.40	(0.49)	0.85	0.88	(3.49)	(0.46)	1.28	0.46
Net asset value
Beginning of period (in usd per share)	16.77	16.37	16.86	16.01	15.13	18.62	19.08	17.80	17.34
End of period (in usd per share)	$ 16.70	$ 16.77	$ 16.37	$ 16.86	$ 16.01	$ 15.13	$ 18.62	$ 19.08	$ 17.80
Ratios and Supplemental Data
Ratio of operating expenses to average net assets	10.32%	9.82%	10.06%	10.31%	11.51%	9.87%	8.61%	6.35%	4.95%
Ratio of operating expenses (excluding interest expense) to average net assets	3.57%	3.52%	4.28%	5.03%	5.43%	4.94%	4.75%	4.72%	4.60%
Ratio of net investment income to average net assets	14.52%	16.07%	13.75%	11.31%	10.74%	8.77%	7.53%	5.51%	2.83%
Portfolio turnover	18.84%	15.65%	13.68%	33.91%	18.81%	22.76%	23.38%	25.42%	23.57%
Total investment return	(1.01%)	55.66%	(15.36%)	18.10%	118.56%	(37.52%)	38.34%	6.61%	27.88%
Total return based on change in NAV	14.73%	17.53%	10.62%	21.05%	19.37%	(3.97%)	9.49%	12.75%	7.21%
Per share market value at the end of the period (in usd per share)	$ 22.32	$ 24.96	$ 17.78	$ 23.73	$ 22.16	$ 11.42	$ 21.04	$ 17.02	$ 16.91
Weighted average common shares outstanding – basic (in shares)	47,448,093	40,727,133	30,015,533	22,840,000	19,060,000	18,000,000	16,074,000	16,074,000	15,825,000
Weighted average common shares outstanding – diluted (in shares)	51,187,714	40,727,133	30,015,533	22,840,000	19,060,000	18,000,000	16,139,000	16,139,000	15,877,000
Common shares outstanding at end of period (in shares)	52,912,796	45,050,759	36,076,000	24,959,000	21,005,000	17,998,000	17,503,000	16,162,000	16,011,000