SIGNIFICANT SUBSIDIARIES - Summarized Financial Information Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2022		Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022		Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021
Investment Company, Nonconsolidated Subsidiary [Line Items]
Cost	$ 1,159,712	[1],[2],[3],[4]			$ 938,303	[5],[6],[7],[8]
Total Investments	1,150,046	[1],[3],[9]			936,614	[5],[7],[10]
Cash and cash equivalents	21,686				11,431
Deferred financing costs and other assets	3,996				4,038
Total assets	1,202,157				973,957
Credit facility	225,000				205,000
Other liabilities	14,568				14,808
Total liabilities	640,670				553,090
Total net assets	561,487		$ 475,724	$ 452,985	420,867		$ 387,337	$ 381,945	$ 368,095	$ 336,251
Total liabilities and net assets	1,202,157				973,957
I-45 SLF LLC
Investment Company, Nonconsolidated Subsidiary [Line Items]
Cost	184,529				187,714
Total Investments	160,998				176,704
Cash and cash equivalents	2,794				9,949
Interest receivable	1,343				850
Accounts receivable	269				123
Deferred financing costs and other assets	831				1,518
Total assets	166,235				189,144
Credit facility	104,000				114,500
Other liabilities	2,654				2,596
Total liabilities	106,654				117,096
Total net assets	59,581				72,048
Total liabilities and net assets	$ 166,235				$ 189,144

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

[2] As of December 31, 2022, the cumulative gross unrealized appreciation for U.S. federal income tax purposes was approximately $66.9 million; cumulative gross unrealized depreciation for federal income tax purposes was $66.7 million. Cumulative net unrealized appreciation was $0.2 million, based on a tax cost of $1,150.6 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 - Fair Value Measurements 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.