Investments - Rollforward of Level 3 Investments Measured at Fair Value (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	$ 359,897	$ 400,195
Funding and purchases of investments, at cost	18,148	28,864
Principal payments and sale proceeds received from investments	(19,732)	(22,324)
Transfers between investments	0
Gross transfers out of Level 3	0	0
Fair value, ending balance	$ 346,824	$ 402,819
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net change in unrealized losses on investments	Net change in unrealized losses on investments
Net change in unrealized gains (losses) on Level 3 investments held	$ (14,800)	$ (3,075)
Amortization and accretion of premiums and discounts, net and end-of term payments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Gain (loss) included in earnings	$ 1,578	$ 1,198
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Interest expense and amortization of fees	Interest expense and amortization of fees
Realized losses on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Gain (loss) included in earnings	$ (3,599)	$ (3,302)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net realized losses on investments	Net realized losses on investments
Net change in unrealized gains (losses) included in earnings
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Gain (loss) included in earnings	$ (10,288)	$ (2,697)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net change in unrealized losses on investments	Net change in unrealized losses on investments
Payment-in-kind coupon
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Gain (loss) included in earnings	$ 820	$ 885
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Interest income from investments	Interest income from investments
Debt Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	$ 318,838	$ 375,025
Funding and purchases of investments, at cost	17,147	27,035
Principal payments and sale proceeds received from investments	(19,440)	(22,318)
Transfers between investments	0
Gross transfers out of Level 3	0	0
Fair value, ending balance	304,515	376,788
Net change in unrealized gains (losses) on Level 3 investments held	(15,134)	(2,713)
Debt Investments | Amortization and accretion of premiums and discounts, net and end-of term payments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Gain (loss) included in earnings	1,578	1,198
Debt Investments | Realized losses on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Gain (loss) included in earnings	(2,962)	(3,208)
Debt Investments | Net change in unrealized gains (losses) included in earnings
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Gain (loss) included in earnings	(11,466)	(1,829)
Debt Investments | Payment-in-kind coupon
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Gain (loss) included in earnings	820	885
Warrant Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	24,111	16,915
Funding and purchases of investments, at cost	409	436
Principal payments and sale proceeds received from investments	(292)	(6)
Transfers between investments	0
Gross transfers out of Level 3	0	0
Fair value, ending balance	24,918	16,390
Net change in unrealized gains (losses) on Level 3 investments held	483	(355)
Warrant Investments | Amortization and accretion of premiums and discounts, net and end-of term payments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Gain (loss) included in earnings	0	0
Warrant Investments | Realized losses on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Gain (loss) included in earnings	(637)	(94)
Warrant Investments | Net change in unrealized gains (losses) included in earnings
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Gain (loss) included in earnings	1,327	(861)
Warrant Investments | Payment-in-kind coupon
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Gain (loss) included in earnings	0	0
Equity Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	16,948	8,255
Funding and purchases of investments, at cost	592	1,393
Principal payments and sale proceeds received from investments	0	0
Transfers between investments	0
Gross transfers out of Level 3	0	0
Fair value, ending balance	17,391	9,641
Net change in unrealized gains (losses) on Level 3 investments held	(149)	(7)
Equity Investments | Amortization and accretion of premiums and discounts, net and end-of term payments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Gain (loss) included in earnings	0	0
Equity Investments | Realized losses on investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Gain (loss) included in earnings	0	0
Equity Investments | Net change in unrealized gains (losses) included in earnings
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Gain (loss) included in earnings	(149)	(7)
Equity Investments | Payment-in-kind coupon
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Gain (loss) included in earnings	0	0
Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Gross transfers out of Level 3	$ 0	$ 0