SUMMARY OF PER SHARE INFORMATION (Details) - $ / shares |
3 Months Ended | 12 Months Ended | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Mar. 31, 2026 |
Dec. 31, 2025 |
Sep. 30, 2025 |
Jun. 30, 2025 |
Mar. 31, 2025 |
Dec. 31, 2024 |
Sep. 30, 2024 |
Jun. 30, 2024 |
Mar. 31, 2026 |
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) | $ 4.06 | $ 4.25 | $ 4.37 | $ 3.97 | $ 3.60 | $ 3.57 | $ 3.45 | $ 3.10 | $ 2.18 | $ 1.48 | ||||||||
| Operating expenses (in usd per share) | (1.67) | (1.74) | (1.65) | (1.67) | (1.70) | (1.78) | (1.76) | (1.62) | (1.16) | (0.87) | ||||||||
| Income taxes (in usd per share) | (0.02) | (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) | $ 0.57 | $ 0.64 | $ 0.57 | $ 0.59 | $ 0.54 | $ 0.63 | $ 0.66 | $ 0.63 | 2.37 | 2.46 | 2.70 | 2.29 | 1.87 | 1.66 | 1.57 | 1.42 | 1.01 | 0.50 |
| Net realized gain (loss), net of tax (in usd per share) | 0.10 | (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) | (0.45) | 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) | (0.04) | (0.01) | (0.01) | 0 | (0.75) | (0.05) | 0 | 0 | 0 | 0 | ||||||||
| Total increase (decrease) from investment operations (in usd per share) | 1.98 | 1.47 | 2.05 | 1.10 | 1.88 | 2.67 | (1.24) | 1.98 | 2.45 | 1.49 | ||||||||
| Accretive (dilutive) effect of share issuances and repurchases (in usd per share) | 0.57 | 0.94 | 0.86 | 0.50 | 1.45 | 0.30 | 0.45 | 0.06 | (0.04) | 0 | ||||||||
| Dividends to shareholders (in usd per share) | (2.56) | (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 | (0.03) | (0.08) | ||||||||
| Issuance of restricted stock (in usd per share) | (0.10) | (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) | (0.04) | (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 | (0.12) | 0.01 | (0.09) | ||||||||
| Share based compensation expense (in usd per share) | 0.08 | 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 | 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 | 0.15 | 0 | 0 | 0 | ||||||||
| Other (in usd per share) | 0.06 | 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) | (0.01) | (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) | 16.75 | 16.62 | 16.59 | 16.70 | 16.59 | 16.59 | 16.60 | 16.77 | 16.70 | 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) | 16.69 | $ 16.75 | $ 16.62 | $ 16.59 | 16.70 | $ 16.59 | $ 16.59 | $ 16.60 | $ 16.69 | $ 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 | 9.95% | 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 | 3.01% | 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 | 14.12% | 14.52% | 16.07% | 13.75% | 11.31% | 10.74% | 8.77% | 7.53% | 5.51% | 2.83% | ||||||||
| Portfolio turnover | 20.02% | 18.84% | 15.65% | 13.68% | 33.91% | 18.81% | 22.76% | 23.38% | 25.42% | 23.57% | ||||||||
| Total investment return | 10.60% | (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 | 15.27% | 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) | $ 22.12 | $ 22.32 | $ 22.12 | $ 22.32 | $ 24.96 | $ 17.78 | $ 23.73 | $ 22.16 | $ 11.42 | $ 21.04 | $ 17.02 | $ 16.91 | ||||||
| Weighted-average basic common shares outstanding (in shares) | 56,529,604 | 47,448,093 | 40,727,133 | 30,016,000 | 22,840,000 | 19,060,000 | 18,000,000 | 16,074,000 | 16,074,000 | 15,825,000 | ||||||||
| Weighted-average diluted common shares outstanding (in shares) | 65,828,805 | 51,187,714 | 40,727,133 | 30,016,000 | 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) | 60,577,181 | 52,912,796 | 60,577,181 | 52,912,796 | 45,051,000 | 36,076,000 | 24,959,000 | 21,005,000 | 17,998,000 | 17,503,000 | 16,162,000 | 16,011,000 | ||||||