SIGNIFICANT SUBSIDIARIES - Summarized Financial Information Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2022		Jun. 30, 2022	Mar. 31, 2022		Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021
Investment Company, Nonconsolidated Subsidiary [Line Items]
Cost	$ 1,064,644	[1],[2],[3],[4]		$ 938,303	[5],[6],[7],[8]
Total Investments	1,056,931	[1],[3],[9]		936,614	[5],[7],[10]
Cash and cash equivalents	30,238			11,431
Debt issuance costs (net of accumulated amortization of $5,090 and $4,573, respectively)	4,044			4,038
Total assets	1,113,171			973,957
Recorded Value	603,329			528,588
Other liabilities	22,434			14,808
Total liabilities	637,447			553,090
Total net assets	475,724		$ 452,985	420,867		$ 381,945	$ 368,095	$ 336,251
Total liabilities and net assets	1,113,171			973,957
I-45 SLF LLC
Investment Company, Nonconsolidated Subsidiary [Line Items]
Cost	188,101			187,714
Total Investments	168,599			176,704
Cash and cash equivalents	5,620			9,949
Accounts receivable	193			123
Debt issuance costs (net of accumulated amortization of $5,090 and $4,573, respectively)	1,037			1,518
Interest Receivable	937			850
Total assets	176,386			189,144
Recorded Value	110,000			114,500
Other liabilities	2,764			2,596
Total liabilities	112,764			117,096
Total net assets	63,622			72,048
Total liabilities and net assets	$ 176,386			$ 189,144

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

[2] As of September 30, 2022, the cumulative gross unrealized appreciation for U.S. federal income tax purposes is approximately $58.9 million; cumulative gross unrealized depreciation for federal income tax purposes is $62.8 million. Cumulative net unrealized depreciation is $3.9 million, based on a tax cost of $1,060.8 million.

[3] 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.

[4] Negative cost in this column represents the original issue discount of certain undrawn revolvers and delayed draw term loans.

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

[6] As of March 31, 2022, the cumulative gross unrealized appreciation for U.S. federal income tax purposes is approximately $67.8 million; cumulative gross unrealized depreciation for federal income tax purposes is $61.7 million. Cumulative net unrealized appreciation is $6.1 million, based on a tax cost of $852.4 million.

[7] 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.

[8] Represents amortized cost. Negative cost in this column represents the original issue discount of certain undrawn revolvers and delayed draw term loans.

[9] 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 for further discussion.

[10] 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 for further discussion.