FAIR VALUE MEASUREMENTS - Level 3 Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023
Fair value measurements
Fair value, beginning of period	$ 673,386	$ 740,068
Funding of investments	207,283	149,424
Non-cash interest income	7,260	5,738
Accretion of discount	4,111	4,493
Proceeds from paydowns and sales	(244,746)	(202,334)
Realized gains (losses)	$ (18,688)	$ (834)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Gain (Loss) on Sale of Investments	Gain (Loss) on Sale of Investments
Net unrealized appreciation (depreciation)	$ (9,134)	$ (23,169)
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Debt and Equity Securities, Unrealized Gain (Loss)	Debt and Equity Securities, Unrealized Gain (Loss)
Fair value, end of period	$ 619,472	$ 673,386
Change in unrealized appreciation (depreciation) on investments still held	(27,059)	(25,471)
First lien secured loans
Fair value measurements
Fair value, beginning of period	553,085	618,267
Funding of investments	206,830	143,792
Non-cash interest income	6,786	5,471
Accretion of discount	4,084	4,411
Proceeds from paydowns and sales	(241,304)	(195,496)
Conversions	(8,852)	(7,232)
Realized gains (losses)	(10,985)	(518)
Net unrealized appreciation (depreciation)	(6,951)	(15,610)
Fair value, end of period	502,693	553,085
Change in unrealized appreciation (depreciation) on investments still held	(17,190)	(17,346)
Second lien secured loans
Fair value measurements
Fair value, beginning of period	19,039	20,634
Non-cash interest income	380	267
Accretion of discount	22	82
Proceeds from paydowns and sales	(2,039)	(233)
Conversions	(11,769)	2,695
Realized gains (losses)	(5,817)	22
Net unrealized appreciation (depreciation)	8,526	(4,428)
Fair value, end of period	8,342	19,039
Change in unrealized appreciation (depreciation) on investments still held	259	(4,430)
Unsecured Loans
Fair value measurements
Fair value, beginning of period	167	167
Non-cash interest income	94
Accretion of discount	5
Conversions	886
Net unrealized appreciation (depreciation)	23
Fair value, end of period	1,175	167
Change in unrealized appreciation (depreciation) on investments still held	23
Subordinated Note to STRS JV
Fair value measurements
Fair value, beginning of period	84,416	80,000
Funding of investments		4,416
Fair value, end of period	84,416	84,416
Equity (excluding STRS JV)
Fair value measurements
Fair value, beginning of period	16,679	21,000
Funding of investments	453	1,216
Proceeds from paydowns and sales	(1,403)	(6,605)
Conversions	19,735	4,537
Realized gains (losses)	(1,886)	(338)
Net unrealized appreciation (depreciation)	(10,732)	(3,131)
Fair value, end of period	22,846	16,679
Change in unrealized appreciation (depreciation) on investments still held	$ (10,151)	$ (3,694)

Indicates line item in statement in which net income is reported that includes unrealized gain (loss) from asset measured at fair value using unobservable input (level 3) and still held.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

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- Definition

Amount of unrealized gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3) and still held.

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
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-Publisher FASB
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- Definition

Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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-Name Accounting Standards Codification
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-SubTopic 10
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

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Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Indicates line item in statement in which net income is reported that includes gain (loss) from asset measured at fair value using unobservable input (level 3).

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The amount of unrealized appreciation (depreciation) on investments still held as at the end of the reporting period.

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Amount of accretion of discount (premium) of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of conversion of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of Non-cash interest income of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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