Fair Value Measurements - Valuation techniques and significant unobservable inputs used in recurring Level 3 fair value measurements of assets and liabilities (Details) $ in Thousands	Mar. 31, 2023 USD ($) item	Dec. 31, 2022 USD ($) item
Fair Value Measurements
Fair Value | $	$ 1,422,873	$ 1,362,488
Loans at fair value where valuation (unadjusted) is obtained from third-party pricing service | $	120,985	106,474
2026 Notes
Fair Value Measurements
Estimated fair value of notes | $	301,552	300,028
Senior Secured Loans | Discounted cash flow | EBITDA multiples
Fair Value Measurements
Fair Value | $	$ 817,101	$ 790,762
Senior Secured Loans | Discounted cash flow | EBITDA multiples | Weighted Average Mean
Fair Value Measurements
Investments, measurement input	0.111	0.107
Senior Secured Loans | Discounted cash flow | EBITDA multiples | Minimum [Member]
Fair Value Measurements
Investments, measurement input	0.040	0.038
Senior Secured Loans | Discounted cash flow | EBITDA multiples | Maximum [Member]
Fair Value Measurements
Investments, measurement input	0.195	0.186
Senior Secured Loans | Discounted cash flow | EBITDA Market Yields | Weighted Average Mean
Fair Value Measurements
Investments, measurement input	0.110	0.109
Senior Secured Loans | Discounted cash flow | EBITDA Market Yields | Minimum [Member]
Fair Value Measurements
Investments, measurement input	0.083	0.087
Senior Secured Loans | Discounted cash flow | EBITDA Market Yields | Maximum [Member]
Fair Value Measurements
Investments, measurement input	0.208	0.223
Senior Secured Loans | Discounted cash flow | Revenue Market Yields | Weighted Average Mean
Fair Value Measurements
Investments, measurement input	0.114	0.115
Senior Secured Loans | Discounted cash flow | Revenue Market Yields | Minimum [Member]
Fair Value Measurements
Investments, measurement input	0.095	0.100
Senior Secured Loans | Discounted cash flow | Revenue Market Yields | Maximum [Member]
Fair Value Measurements
Investments, measurement input	0.166	0.216
Senior Secured Loans | Discounted cash flow | Revenue multiples
Fair Value Measurements
Fair Value | $	$ 380,294	$ 354,158
Senior Secured Loans | Discounted cash flow | Revenue multiples | Weighted Average Mean
Fair Value Measurements
Investments, measurement input	0.073	0.073
Senior Secured Loans | Discounted cash flow | Revenue multiples | Minimum [Member]
Fair Value Measurements
Investments, measurement input	0.014	0.014
Senior Secured Loans | Discounted cash flow | Revenue multiples | Maximum [Member]
Fair Value Measurements
Investments, measurement input	0.200	0.200
Senior Secured Loans | Enterprise value | Book value multiples
Fair Value Measurements
Fair Value | $	$ 2,376
Senior Secured Loans | Enterprise value | Book value multiples | Weighted Average Mean
Fair Value Measurements
Investments, measurement input	0.008
Senior Secured Loans | Enterprise value | Book value multiples | Minimum [Member]
Fair Value Measurements
Investments, measurement input	0.008
Senior Secured Loans | Enterprise value | Book value multiples | Maximum [Member]
Fair Value Measurements
Investments, measurement input	0.008
Unitranche Secured Loans | Discounted cash flow | EBITDA multiples
Fair Value Measurements
Fair Value | $	$ 95,974	$ 95,341
Unitranche Secured Loans | Discounted cash flow | EBITDA multiples | Weighted Average Mean
Fair Value Measurements
Investments, measurement input	0.097	0.099
Unitranche Secured Loans | Discounted cash flow | EBITDA multiples | Minimum [Member]
Fair Value Measurements
Investments, measurement input	0.083	0.085
Unitranche Secured Loans | Discounted cash flow | EBITDA multiples | Maximum [Member]
Fair Value Measurements
Investments, measurement input	0.145	0.155
Unitranche Secured Loans | Discounted cash flow | EBITDA Market Yields | Weighted Average Mean
Fair Value Measurements
Investments, measurement input	0.145	0.121
Unitranche Secured Loans | Discounted cash flow | EBITDA Market Yields | Minimum [Member]
Fair Value Measurements
Investments, measurement input	0.087	0.092
Unitranche Secured Loans | Discounted cash flow | EBITDA Market Yields | Maximum [Member]
Fair Value Measurements
Investments, measurement input	0.251	0.138
Unitranche Secured Loans | Discounted cash flow | Revenue Market Yields | Weighted Average Mean
Fair Value Measurements
Investments, measurement input	0.114	0.118
Unitranche Secured Loans | Discounted cash flow | Revenue Market Yields | Minimum [Member]
Fair Value Measurements
Investments, measurement input	0.112	0.116
Unitranche Secured Loans | Discounted cash flow | Revenue Market Yields | Maximum [Member]
Fair Value Measurements
Investments, measurement input	0.117	0.121
Unitranche Secured Loans | Discounted cash flow | Revenue multiples
Fair Value Measurements
Fair Value | $	$ 32,406	$ 32,037
Unitranche Secured Loans | Discounted cash flow | Revenue multiples | Weighted Average Mean
Fair Value Measurements
Investments, measurement input	0.094	0.093
Unitranche Secured Loans | Discounted cash flow | Revenue multiples | Minimum [Member]
Fair Value Measurements
Investments, measurement input	0.060	0.058
Unitranche Secured Loans | Discounted cash flow | Revenue multiples | Maximum [Member]
Fair Value Measurements
Investments, measurement input	0.125	0.125
Junior Secured Loans | Discounted cash flow | Market yields
Fair Value Measurements
Fair Value | $	$ 44,633	$ 44,469
Junior Secured Loans | Discounted cash flow | Market yields | Weighted Average Mean
Fair Value Measurements
Investments, measurement input	0.130	0.137
Junior Secured Loans | Discounted cash flow | Market yields | Minimum [Member]
Fair Value Measurements
Investments, measurement input	0.124	0.123
Junior Secured Loans | Discounted cash flow | Market yields | Maximum [Member]
Fair Value Measurements
Investments, measurement input	0.156	0.204
Equity Securities | Enterprise value | EBITDA multiples
Fair Value Measurements
Fair Value | $	$ 35,515	$ 31,060
Equity Securities | Enterprise value | EBITDA multiples | Weighted Average Mean
Fair Value Measurements
Investments, measurement input	0.118	0.109
Equity Securities | Enterprise value | EBITDA multiples | Minimum [Member]
Fair Value Measurements
Investments, measurement input	0.040	0.038
Equity Securities | Enterprise value | EBITDA multiples | Maximum [Member]
Fair Value Measurements
Investments, measurement input	0.186	0.179
Equity Securities | Enterprise value | Revenue multiples
Fair Value Measurements
Fair Value | $	$ 13,172	$ 13,400
Equity Securities | Enterprise value | Revenue multiples | Weighted Average Mean
Fair Value Measurements
Investments, measurement input	0.052	0.051
Equity Securities | Enterprise value | Revenue multiples | Minimum [Member]
Fair Value Measurements
Investments, measurement input	0.014	0.019
Equity Securities | Enterprise value | Revenue multiples | Maximum [Member]
Fair Value Measurements
Investments, measurement input	0.113	0.123
Equity Securities | Option pricing model | Volatility
Fair Value Measurements
Fair Value | $	$ 1,402	$ 1,261
Equity Securities | Option pricing model | Volatility | Weighted Average Mean
Fair Value Measurements
Investments, measurement input	0.629	0.751
Equity Securities | Option pricing model | Volatility | Minimum [Member]
Fair Value Measurements
Investments, measurement input	0.450	0.494
Equity Securities | Option pricing model | Volatility | Maximum [Member]
Fair Value Measurements
Investments, measurement input	0.740	1.264