FAIR VALUE MEASUREMENTS - Measurement Inputs and Valuation Techniques (Details) $ in Thousands	Sep. 30, 2023 USD ($)		Mar. 31, 2023 USD ($)
Fair Value
Investments at fair value	$ 1,353,566	[1],[2],[3]	$ 1,206,388	[4],[5],[6]
Significant Unobservable Inputs (Level 3)
Fair Value
Investments at fair value	1,300,144
Significant Unobservable Inputs (Level 3) | First lien loans | Income Approach
Fair Value
Investments at fair value	$ 1,086,345		$ 953,918
Significant Unobservable Inputs (Level 3) | First lien loans | Income Approach | Minimum | Discount Rate
Fair​ Value Measurement Input
Investments, measurement input	0.058		0.069
Significant Unobservable Inputs (Level 3) | First lien loans | Income Approach | Minimum | Third Party Broker Quote
Fair​ Value Measurement Input
Investments, measurement input	94.0		5.1
Significant Unobservable Inputs (Level 3) | First lien loans | Income Approach | Maximum | Discount Rate
Fair​ Value Measurement Input
Investments, measurement input	0.454		0.262
Significant Unobservable Inputs (Level 3) | First lien loans | Income Approach | Maximum | Third Party Broker Quote
Fair​ Value Measurement Input
Investments, measurement input	94.0		96.5
Significant Unobservable Inputs (Level 3) | First lien loans | Income Approach | Weighted Average | Discount Rate
Fair​ Value Measurement Input
Investments, measurement input	0.136		0.130
Significant Unobservable Inputs (Level 3) | First lien loans | Income Approach | Weighted Average | Third Party Broker Quote
Fair​ Value Measurement Input
Investments, measurement input	94.0		93.9
Significant Unobservable Inputs (Level 3) | First lien loans | Market Approach
Fair Value
Investments at fair value	$ 54,935		$ 41,923
Significant Unobservable Inputs (Level 3) | First lien loans | Market Approach | Minimum | Cost
Fair​ Value Measurement Input
Investments, measurement input	98.0		94.1
Significant Unobservable Inputs (Level 3) | First lien loans | Market Approach | Maximum | Cost
Fair​ Value Measurement Input
Investments, measurement input	98.5		98.1
Significant Unobservable Inputs (Level 3) | First lien loans | Market Approach | Weighted Average | Cost
Fair​ Value Measurement Input
Investments, measurement input	98.1		97.9
Significant Unobservable Inputs (Level 3) | First lien loans | Enterprise Value Waterfall Approach
Fair Value
Investments at fair value			$ 5,143
Significant Unobservable Inputs (Level 3) | First lien loans | Enterprise Value Waterfall Approach | Minimum | Discount Rate
Fair​ Value Measurement Input
Investments, measurement input			0.272
Significant Unobservable Inputs (Level 3) | First lien loans | Enterprise Value Waterfall Approach | Minimum | EBITDA Multiple
Fair​ Value Measurement Input
Investments, measurement input			9.4
Significant Unobservable Inputs (Level 3) | First lien loans | Enterprise Value Waterfall Approach | Maximum | Discount Rate
Fair​ Value Measurement Input
Investments, measurement input			0.272
Significant Unobservable Inputs (Level 3) | First lien loans | Enterprise Value Waterfall Approach | Maximum | EBITDA Multiple
Fair​ Value Measurement Input
Investments, measurement input			9.4
Significant Unobservable Inputs (Level 3) | First lien loans | Enterprise Value Waterfall Approach | Weighted Average | Discount Rate
Fair​ Value Measurement Input
Investments, measurement input			0.272
Significant Unobservable Inputs (Level 3) | First lien loans | Enterprise Value Waterfall Approach | Weighted Average | EBITDA Multiple
Fair​ Value Measurement Input
Investments, measurement input			9.4
Significant Unobservable Inputs (Level 3) | Second lien loans | Income Approach
Fair Value
Investments at fair value	$ 37,034		$ 32,226
Significant Unobservable Inputs (Level 3) | Second lien loans | Income Approach | Minimum | Discount Rate
Fair​ Value Measurement Input
Investments, measurement input	0.132		0.183
Significant Unobservable Inputs (Level 3) | Second lien loans | Income Approach | Minimum | Third Party Broker Quote
Fair​ Value Measurement Input
Investments, measurement input	52.5		61.3
Significant Unobservable Inputs (Level 3) | Second lien loans | Income Approach | Maximum | Discount Rate
Fair​ Value Measurement Input
Investments, measurement input	0.314		0.343
Significant Unobservable Inputs (Level 3) | Second lien loans | Income Approach | Maximum | Third Party Broker Quote
Fair​ Value Measurement Input
Investments, measurement input	52.5		61.3
Significant Unobservable Inputs (Level 3) | Second lien loans | Income Approach | Weighted Average | Discount Rate
Fair​ Value Measurement Input
Investments, measurement input	0.221		0.251
Significant Unobservable Inputs (Level 3) | Second lien loans | Income Approach | Weighted Average | Third Party Broker Quote
Fair​ Value Measurement Input
Investments, measurement input	52.5		61.3
Significant Unobservable Inputs (Level 3) | Second lien loans | Enterprise Value Waterfall Approach
Fair Value
Investments at fair value			$ 3,594
Significant Unobservable Inputs (Level 3) | Second lien loans | Enterprise Value Waterfall Approach | Minimum | Discount Rate
Fair​ Value Measurement Input
Investments, measurement input			0.272
Significant Unobservable Inputs (Level 3) | Second lien loans | Enterprise Value Waterfall Approach | Minimum | EBITDA Multiple
Fair​ Value Measurement Input
Investments, measurement input			9.4
Significant Unobservable Inputs (Level 3) | Second lien loans | Enterprise Value Waterfall Approach | Maximum | Discount Rate
Fair​ Value Measurement Input
Investments, measurement input			0.272
Significant Unobservable Inputs (Level 3) | Second lien loans | Enterprise Value Waterfall Approach | Maximum | EBITDA Multiple
Fair​ Value Measurement Input
Investments, measurement input			9.4
Significant Unobservable Inputs (Level 3) | Second lien loans | Enterprise Value Waterfall Approach | Weighted Average | Discount Rate
Fair​ Value Measurement Input
Investments, measurement input			0.272
Significant Unobservable Inputs (Level 3) | Second lien loans | Enterprise Value Waterfall Approach | Weighted Average | EBITDA Multiple
Fair​ Value Measurement Input
Investments, measurement input			9.4
Significant Unobservable Inputs (Level 3) | Subordinated debt | Market Approach
Fair Value
Investments at fair value	$ 202		$ 205
Significant Unobservable Inputs (Level 3) | Subordinated debt | Market Approach | Minimum | Cost
Fair​ Value Measurement Input
Investments, measurement input	100.0		100.0
Significant Unobservable Inputs (Level 3) | Subordinated debt | Market Approach | Maximum | Cost
Fair​ Value Measurement Input
Investments, measurement input	100.0		100.0
Significant Unobservable Inputs (Level 3) | Subordinated debt | Market Approach | Weighted Average | Cost
Fair​ Value Measurement Input
Investments, measurement input	1.000		100.0
Significant Unobservable Inputs (Level 3) | Subordinated debt | Enterprise Value Waterfall Approach
Fair Value
Investments at fair value	$ 558		$ 586
Significant Unobservable Inputs (Level 3) | Subordinated debt | Enterprise Value Waterfall Approach | Minimum | Discount Rate
Fair​ Value Measurement Input
Investments, measurement input	0.148		0.202
Significant Unobservable Inputs (Level 3) | Subordinated debt | Enterprise Value Waterfall Approach | Minimum | EBITDA Multiple
Fair​ Value Measurement Input
Investments, measurement input	6.0		6.0
Significant Unobservable Inputs (Level 3) | Subordinated debt | Enterprise Value Waterfall Approach | Maximum | Discount Rate
Fair​ Value Measurement Input
Investments, measurement input	0.253		0.250
Significant Unobservable Inputs (Level 3) | Subordinated debt | Enterprise Value Waterfall Approach | Maximum | EBITDA Multiple
Fair​ Value Measurement Input
Investments, measurement input	7.7		7.7
Significant Unobservable Inputs (Level 3) | Subordinated debt | Enterprise Value Waterfall Approach | Weighted Average | Discount Rate
Fair​ Value Measurement Input
Investments, measurement input	0.181		0.218
Significant Unobservable Inputs (Level 3) | Subordinated debt | Enterprise Value Waterfall Approach | Weighted Average | EBITDA Multiple
Fair​ Value Measurement Input
Investments, measurement input	6.5		6.6
Significant Unobservable Inputs (Level 3) | Preferred equity | Market Approach
Fair Value
Investments at fair value	$ 2,000		$ 3,875
Significant Unobservable Inputs (Level 3) | Preferred equity | Market Approach | Minimum | Cost
Fair​ Value Measurement Input
Investments, measurement input	100.0		100.0
Significant Unobservable Inputs (Level 3) | Preferred equity | Market Approach | Maximum | Cost
Fair​ Value Measurement Input
Investments, measurement input	100.0		100.0
Significant Unobservable Inputs (Level 3) | Preferred equity | Market Approach | Weighted Average | Cost
Fair​ Value Measurement Input
Investments, measurement input	100.0		100.0
Significant Unobservable Inputs (Level 3) | Preferred equity | Enterprise Value Waterfall Approach
Fair Value
Investments at fair value	$ 64,440		$ 59,518
Significant Unobservable Inputs (Level 3) | Preferred equity | Enterprise Value Waterfall Approach | Minimum | Discount Rate
Fair​ Value Measurement Input
Investments, measurement input	0.127		0.117
Significant Unobservable Inputs (Level 3) | Preferred equity | Enterprise Value Waterfall Approach | Minimum | EBITDA Multiple
Fair​ Value Measurement Input
Investments, measurement input	4.8		4.7
Significant Unobservable Inputs (Level 3) | Preferred equity | Enterprise Value Waterfall Approach | Maximum | Discount Rate
Fair​ Value Measurement Input
Investments, measurement input	0.309		0.308
Significant Unobservable Inputs (Level 3) | Preferred equity | Enterprise Value Waterfall Approach | Maximum | EBITDA Multiple
Fair​ Value Measurement Input
Investments, measurement input	15.9		16.7
Significant Unobservable Inputs (Level 3) | Preferred equity | Enterprise Value Waterfall Approach | Weighted Average | Discount Rate
Fair​ Value Measurement Input
Investments, measurement input	0.190		0.171
Significant Unobservable Inputs (Level 3) | Preferred equity | Enterprise Value Waterfall Approach | Weighted Average | EBITDA Multiple
Fair​ Value Measurement Input
Investments, measurement input	9.9		9.8
Significant Unobservable Inputs (Level 3) | Common equity & warrants | Market Approach
Fair Value
Investments at fair value			$ 1,080
Significant Unobservable Inputs (Level 3) | Common equity & warrants | Market Approach | Minimum | Exit Value
Fair​ Value Measurement Input
Investments, measurement input			100.0
Significant Unobservable Inputs (Level 3) | Common equity & warrants | Market Approach | Maximum | Exit Value
Fair​ Value Measurement Input
Investments, measurement input			100.0
Significant Unobservable Inputs (Level 3) | Common equity & warrants | Market Approach | Weighted Average | Exit Value
Fair​ Value Measurement Input
Investments, measurement input			100.0
Significant Unobservable Inputs (Level 3) | Common equity & warrants | Enterprise Value Waterfall Approach
Fair Value
Investments at fair value	$ 54,630		$ 53,064
Significant Unobservable Inputs (Level 3) | Common equity & warrants | Enterprise Value Waterfall Approach | Minimum | Discount Rate
Fair​ Value Measurement Input
Investments, measurement input	0.120		0.114
Significant Unobservable Inputs (Level 3) | Common equity & warrants | Enterprise Value Waterfall Approach | Minimum | EBITDA Multiple
Fair​ Value Measurement Input
Investments, measurement input	5.2		5.5
Significant Unobservable Inputs (Level 3) | Common equity & warrants | Enterprise Value Waterfall Approach | Maximum | Discount Rate
Fair​ Value Measurement Input
Investments, measurement input	0.268		0.366
Significant Unobservable Inputs (Level 3) | Common equity & warrants | Enterprise Value Waterfall Approach | Maximum | EBITDA Multiple
Fair​ Value Measurement Input
Investments, measurement input	17.3		18.6
Significant Unobservable Inputs (Level 3) | Common equity & warrants | Enterprise Value Waterfall Approach | Weighted Average | Discount Rate
Fair​ Value Measurement Input
Investments, measurement input	0.166		0.182
Significant Unobservable Inputs (Level 3) | Common equity & warrants | Enterprise Value Waterfall Approach | Weighted Average | EBITDA Multiple
Fair​ Value Measurement Input
Investments, measurement input	9.1		9.5

[1] All debt investments are income-producing, unless otherwise noted. Equity investments are non-income producing, unless otherwise noted.

[2] Equity ownership may be held in shares or units of a company that is either wholly owned by the portfolio company or under common control by the same parent company to the portfolio company.

[3] The Company's investment portfolio is comprised entirely of debt and equity securities of privately held companies for which quoted prices falling within the categories of Level 1 and Level 2 inputs are not readily available. Therefore, the Company values all of its portfolio investments at fair value, as determined in good faith by the valuation committee comprised of certain officers of the Company (the "Valuation Committee") as the valuation designee of the Board of Directors (the "Valuation Designee") pursuant to Rule 2a-5 under the Investment Company Act of 1940, as amended (the “1940 Act”), using significant unobservable Level 3 inputs. Refer to Note 4 - Fair Value Measurements for further discussion.

[4] All debt investments are income-producing, unless otherwise noted. Equity investments are non-income producing, unless otherwise noted.

[5] Equity ownership may be held in shares or units of a company that is either wholly owned by the portfolio company or under common control by the same parent company to the portfolio company.

[6] The Company's investment portfolio is comprised entirely of debt and equity securities of privately held companies for which quoted prices falling within the categories of Level 1 and Level 2 inputs are not readily available. Therefore, the Company values all of its portfolio investments at fair value, as determined in good faith by the Board of Directors, using significant unobservable Level 3 inputs. Refer to Note 4 - Fair Value Measurements to our audited consolidated financial statements for further discussion.