| In millions, except per share items | Jun-30-23 | Sep-30-22 | Jun-30-22 | Mar-31-22 | Dec-31-21 | Sep-30-21 | Jun-30-21 | Mar-31-21 |
| | 10-Q | 8-K | 10-Q | 10-Q | 10-K | 10-Q | 10-Q | 10-Q |
| Investment Income, Net [Abstract] | | | | | | | | |
| Interest and Other Income [Abstract] | | | | | | | | |
| Investment Income, Interest | | | 27.0 | | | | | |
| Noninterest Income | | | -22.7 | 4.5 | 3.6 | 12.1 | 10.4 | 10.2 |
| Gross Investment Income, Operating | | | 27.4 | | | | | |
| |
| Operating Expenses [Abstract] | | | | | | | | |
| Base management fee | | | 3.9 | | | | | |
| Income incentive fee | | | 3.2 | | | | | |
| Interest Expense, Debt | | | 6.1 | | | | | |
| Other Expenses | | | 0.5 | | | | | |
| General and Administrative Expense | | 4.3 | 4.4 | 4.1 | 4.1 | 4.7 | 4.2 | 4.6 |
| Operating Expenses | | 0.4 | 10.7 | 6.9 | 4.1 | 44.9 | 44.5 | 45.8 |
| Net Investment Income | | 56.0 | 49.0 | 45.7 | 41.1 | 40.1 | 42.4 | 44.5 |
| |
| Realized and Unrealized Gain (Loss), Investment and Derivative, Operating, before Tax [Abstract] | | | | | | | | |
| Realized Investment Gains (Losses) | | | -27.1 | | | | | |
| |
| Unrealized Gain (Loss) on Investments | | | | | | | | |
| Gain (Loss) on Extinguishment of Debt | | | | | | | | |
| Gain (Loss) on Investments | | | -27.1 | | | | | |
| Net Income (Loss) | | | -14.4 | | | | | |
| Net Income (Loss) Attributable to Parent, Total | | | -14.4 | | | | | |
| |
| Diluted net investment income per share of common stock (in dollars per share) | | | $0.41 | | | | | |
| Basic net investment income per share of common stock (in dollars per share) | | | $0.41 | | | | | |
| Net increase (decrease) in net assets resulting from operations per share of common stock | | | 0.0 | | | | | |
| |
| Basic weighted average shares of common stock outstanding (in shares) | | 31.6 | 31.0 | 31.0 | 30.9 | 30.8 | 30.8 | 30.7 |
| Diluted weighted average shares of common stock outstanding (in shares) | | 31.6 | 31.0 | 31.0 | 30.9 | 30.8 | 30.8 | 30.7 |
| |
| Regular Distributions Declared Per Share | | | | | | | | |
| Special Distributions Declared, Per Share | | | | | | | | |
| Earnings Per Share, Diluted, Distributed | | | 0.0 | | | | | |
| Earnings Per Share, Basic, Distributed | | | 0.0 | | | | | |