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Fair Value of Financial Instruments - Level 3 Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Level 3 assets, beginning balance			$ 469,753	$ 441,508
Purchase and origination of portfolio investments			34,721	129,554
Proceeds from principal payments on portfolio investments			(46,288)	(68,805)
Sale and redemption of portfolio investments			(2,710)	(5,986)
Proceeds from distributions received from portfolio investments			(10,610)	(14,261)
Transfers out of Level 3	$ (5,957)	$ (6,403)	(7,491)	(6,403)
Transfers into Level 3	0	0	0	3,252
Level 3 assets, ending balance	435,581	470,125	435,581	470,125
Net unrealized depreciation on investments held			(12,885)	(15,817)
Realized gain (loss) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			(15,992)	(179)
Unrealized gain (loss) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			3,175	(17,896)
Amortization of Net Loan Fees
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			1,164	1,250
Accretion of interest income on Structured Finance Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			8,534	7,647
Capitalized PIK interest and dividends
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			1,491	650
Amendment fees received
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			(166)	(206)
Senior Secured Debt Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Level 3 assets, beginning balance			280,813	261,113
Purchase and origination of portfolio investments			26,378	85,066
Proceeds from principal payments on portfolio investments			(37,777)	(51,060)
Sale and redemption of portfolio investments			(2,710)	(2,845)
Proceeds from distributions received from portfolio investments			0	0
Transfers out of Level 3			(7,491)	(6,403)
Transfers into Level 3				3,252
Level 3 assets, ending balance	257,478	280,799	257,478	280,799
Net unrealized depreciation on investments held			(4,125)	(8,941)
Senior Secured Debt Investments | Realized gain (loss) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			(140)	(122)
Senior Secured Debt Investments | Unrealized gain (loss) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			(3,110)	(9,416)
Senior Secured Debt Investments | Amortization of Net Loan Fees
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			994	1,058
Senior Secured Debt Investments | Accretion of interest income on Structured Finance Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			0	0
Senior Secured Debt Investments | Capitalized PIK interest and dividends
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			687	362
Senior Secured Debt Investments | Amendment fees received
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			(166)	(206)
Subordinated debt investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Level 3 assets, beginning balance			1,226	17,943
Purchase and origination of portfolio investments			0	0
Proceeds from principal payments on portfolio investments			0	(8,245)
Sale and redemption of portfolio investments			0	0
Proceeds from distributions received from portfolio investments			0	0
Transfers out of Level 3			0	0
Transfers into Level 3				0
Level 3 assets, ending balance	100	4,274	100	4,274
Net unrealized depreciation on investments held			(22)	(5,487)
Subordinated debt investments | Realized gain (loss) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			(9,210)	0
Subordinated debt investments | Unrealized gain (loss) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			8,084	(5,488)
Subordinated debt investments | Amortization of Net Loan Fees
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			0	6
Subordinated debt investments | Accretion of interest income on Structured Finance Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			0	0
Subordinated debt investments | Capitalized PIK interest and dividends
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			0	58
Subordinated debt investments | Amendment fees received
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			0	0
Preferred equity
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Level 3 assets, beginning balance			8,196	3,765
Purchase and origination of portfolio investments			345	0
Proceeds from principal payments on portfolio investments			0	0
Sale and redemption of portfolio investments			0	0
Proceeds from distributions received from portfolio investments			0	0
Transfers out of Level 3			0	0
Transfers into Level 3				0
Level 3 assets, ending balance	11,806	7,502	11,806	7,502
Net unrealized depreciation on investments held			2,474	3,507
Preferred equity | Realized gain (loss) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			0	(51)
Preferred equity | Unrealized gain (loss) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			2,461	3,558
Preferred equity | Amortization of Net Loan Fees
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			0	0
Preferred equity | Accretion of interest income on Structured Finance Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			0	0
Preferred equity | Capitalized PIK interest and dividends
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			804	230
Preferred equity | Amendment fees received
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			0	0
Common equity, warrants and other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Level 3 assets, beginning balance			91,000	83,486
Purchase and origination of portfolio investments			356	1,290
Proceeds from principal payments on portfolio investments			0	0
Sale and redemption of portfolio investments			0	(3,141)
Proceeds from distributions received from portfolio investments			(962)	0
Transfers out of Level 3			0	0
Transfers into Level 3				0
Level 3 assets, ending balance	82,908	87,679	82,908	87,679
Net unrealized depreciation on investments held			(7,590)	7,657
Common equity, warrants and other | Realized gain (loss) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			(6,642)	(6)
Common equity, warrants and other | Unrealized gain (loss) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			(844)	6,050
Common equity, warrants and other | Amortization of Net Loan Fees
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			0	0
Common equity, warrants and other | Accretion of interest income on Structured Finance Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			0	0
Common equity, warrants and other | Capitalized PIK interest and dividends
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			0	0
Common equity, warrants and other | Amendment fees received
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			0	0
Structured Finance Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Level 3 assets, beginning balance			88,518	75,201
Purchase and origination of portfolio investments			7,642	43,198
Proceeds from principal payments on portfolio investments			(8,511)	(9,500)
Sale and redemption of portfolio investments			0	0
Proceeds from distributions received from portfolio investments			(9,648)	(14,261)
Transfers out of Level 3			0	0
Transfers into Level 3				0
Level 3 assets, ending balance	$ 83,289	$ 89,871	83,289	89,871
Net unrealized depreciation on investments held			(3,622)	(12,553)
Structured Finance Securities | Realized gain (loss) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			0	0
Structured Finance Securities | Unrealized gain (loss) on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			(3,416)	(12,600)
Structured Finance Securities | Amortization of Net Loan Fees
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			170	186
Structured Finance Securities | Accretion of interest income on Structured Finance Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			8,534	7,647
Structured Finance Securities | Capitalized PIK interest and dividends
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			0	0
Structured Finance Securities | Amendment fees received
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Amounts included in earnings			$ 0	$ 0

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Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Distributions

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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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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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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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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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Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

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