Commitment and Contingencies - Unfunded Commitments (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Debt Securities
Other Commitments [Line Items]
Unfunded commitments	$ 952.4	$ 1,724.1
Unfunded Equity/Other commitments
Other Commitments [Line Items]
Unfunded commitments	475.3	$ 576.9
Investment, Identifier [Axis]: 3Pillar Global Inc 1
Other Commitments [Line Items]
Unfunded commitments	9.2
Investment, Identifier [Axis]: 3Pillar Global Inc 2
Other Commitments [Line Items]
Unfunded commitments	24.9
Investment, Identifier [Axis]: 48Forty Solutions LLC
Other Commitments [Line Items]
Unfunded commitments	10.6
Investment, Identifier [Axis]: Advanced Dermatology & Cosmetic Surgery 1
Other Commitments [Line Items]
Unfunded commitments	2.2
Investment, Identifier [Axis]: Advanced Dermatology & Cosmetic Surgery 2
Other Commitments [Line Items]
Unfunded commitments	3.6
Investment, Identifier [Axis]: Affordable Care Inc 1
Other Commitments [Line Items]
Unfunded commitments	28.4
Investment, Identifier [Axis]: Affordable Care Inc 2
Other Commitments [Line Items]
Unfunded commitments	11.4
Investment, Identifier [Axis]: Alacrity Solutions Group LLC
Other Commitments [Line Items]
Unfunded commitments	10.6
Investment, Identifier [Axis]: American Vision Partners
Other Commitments [Line Items]
Unfunded commitments	7.8
Investment, Identifier [Axis]: Amerivet Partners Management Inc 1
Other Commitments [Line Items]
Unfunded commitments	8.4
Investment, Identifier [Axis]: Amerivet Partners Management Inc 2
Other Commitments [Line Items]
Unfunded commitments	50.1
Investment, Identifier [Axis]: Arcfield Acquisition Corp
Other Commitments [Line Items]
Unfunded commitments	7.1
Investment, Identifier [Axis]: Arcos LLC/VA
Other Commitments [Line Items]
Unfunded commitments	4.5
Investment, Identifier [Axis]: AxiomSL Ltd 1
Other Commitments [Line Items]
Unfunded commitments	2.4
Investment, Identifier [Axis]: AxiomSL Ltd 2
Other Commitments [Line Items]
Unfunded commitments	2.3
Investment, Identifier [Axis]: BGB Group LLC
Other Commitments [Line Items]
Unfunded commitments	19.9
Investment, Identifier [Axis]: Barbri Inc
Other Commitments [Line Items]
Unfunded commitments	9.1
Investment, Identifier [Axis]: Byrider Finance LLC, Structured Mezzanine
Other Commitments [Line Items]
Unfunded commitments	6.8
Investment, Identifier [Axis]: CFC Underwriting Ltd
Other Commitments [Line Items]
Unfunded commitments	5.7
Investment, Identifier [Axis]: CSafe Global
Other Commitments [Line Items]
Unfunded commitments	34.9
Investment, Identifier [Axis]: Callodine Commercial Finance LLC, 2L Term Loan B
Other Commitments [Line Items]
Unfunded commitments	36.1
Investment, Identifier [Axis]: Clarience Technologies LLC
Other Commitments [Line Items]
Unfunded commitments	25.3
Investment, Identifier [Axis]: Community Brands Inc 1
Other Commitments [Line Items]
Unfunded commitments	3.8
Investment, Identifier [Axis]: Community Brands Inc 2
Other Commitments [Line Items]
Unfunded commitments	1.9
Investment, Identifier [Axis]: Corsearch Intermediate Inc
Other Commitments [Line Items]
Unfunded commitments	4.4
Investment, Identifier [Axis]: DOC Generici Srl
Other Commitments [Line Items]
Unfunded commitments	2.3
Investment, Identifier [Axis]: Dental Care Alliance Inc
Other Commitments [Line Items]
Unfunded commitments	1.7
Investment, Identifier [Axis]: Encora Digital Inc
Other Commitments [Line Items]
Unfunded commitments	19.4
Investment, Identifier [Axis]: Envirotainer Ltd
Other Commitments [Line Items]
Unfunded commitments	2.7
Investment, Identifier [Axis]: Excelitas Technologies Corp 1
Other Commitments [Line Items]
Unfunded commitments	1.0
Investment, Identifier [Axis]: Excelitas Technologies Corp 2
Other Commitments [Line Items]
Unfunded commitments	4.7
Investment, Identifier [Axis]: Follett Software Co
Other Commitments [Line Items]
Unfunded commitments	9.9
Investment, Identifier [Axis]: Foundation Consumer Brands LLC
Other Commitments [Line Items]
Unfunded commitments	6.6
Investment, Identifier [Axis]: Foundation Risk Partners Corp
Other Commitments [Line Items]
Unfunded commitments	4.1
Investment, Identifier [Axis]: Galway Partners Holdings LLC 1
Other Commitments [Line Items]
Unfunded commitments	11.8
Investment, Identifier [Axis]: Galway Partners Holdings LLC 2
Other Commitments [Line Items]
Unfunded commitments	1.3
Investment, Identifier [Axis]: Gigamon Inc
Other Commitments [Line Items]
Unfunded commitments	9.3
Investment, Identifier [Axis]: HKA
Other Commitments [Line Items]
Unfunded commitments	0.2
Investment, Identifier [Axis]: HM Dunn Co Inc
Other Commitments [Line Items]
Unfunded commitments	2.0
Investment, Identifier [Axis]: Heniff Transportation Systems LLC
Other Commitments [Line Items]
Unfunded commitments	17.6
Investment, Identifier [Axis]: Higginbotham Insurance Agency Inc
Other Commitments [Line Items]
Unfunded commitments	6.0
Investment, Identifier [Axis]: Individual FoodService
Other Commitments [Line Items]
Unfunded commitments	1.4
Investment, Identifier [Axis]: Individual FoodService 1
Other Commitments [Line Items]
Unfunded commitments	4.7
Investment, Identifier [Axis]: Insight Global LLC 1
Other Commitments [Line Items]
Unfunded commitments	12.6
Investment, Identifier [Axis]: Insight Global LLC 2
Other Commitments [Line Items]
Unfunded commitments	26.8
Investment, Identifier [Axis]: J S Held LLC 1
Other Commitments [Line Items]
Unfunded commitments	5.2
Investment, Identifier [Axis]: J S Held LLC 2
Other Commitments [Line Items]
Unfunded commitments	19.2
Investment, Identifier [Axis]: Jet Edge International LLC, Term Loan
Other Commitments [Line Items]
Unfunded commitments	0.7
Investment, Identifier [Axis]: Karman Space Inc
Other Commitments [Line Items]
Unfunded commitments	1.0
Investment, Identifier [Axis]: Lakefield Veterinary Group
Other Commitments [Line Items]
Unfunded commitments	35.2
Investment, Identifier [Axis]: Lakeview Farms Inc 1
Other Commitments [Line Items]
Unfunded commitments	10.8
Investment, Identifier [Axis]: Lakeview Farms Inc 2
Other Commitments [Line Items]
Unfunded commitments	2.3
Investment, Identifier [Axis]: Lexitas Inc
Other Commitments [Line Items]
Unfunded commitments	8.4
Investment, Identifier [Axis]: Lipari Foods LLC
Other Commitments [Line Items]
Unfunded commitments	27.3
Investment, Identifier [Axis]: Lloyd's Register Quality Assurance Ltd
Other Commitments [Line Items]
Unfunded commitments	12.6
Investment, Identifier [Axis]: Magna Legal Services LLC 1
Other Commitments [Line Items]
Unfunded commitments	2.2
Investment, Identifier [Axis]: Magna Legal Services LLC 2
Other Commitments [Line Items]
Unfunded commitments	5.2
Investment, Identifier [Axis]: Med-Metrix 1
Other Commitments [Line Items]
Unfunded commitments	25.0
Investment, Identifier [Axis]: Med-Metrix 2
Other Commitments [Line Items]
Unfunded commitments	7.8
Investment, Identifier [Axis]: Monitronics International Inc
Other Commitments [Line Items]
Unfunded commitments	23.9
Investment, Identifier [Axis]: Motion Recruitment Partners LLC
Other Commitments [Line Items]
Unfunded commitments	59.6
Investment, Identifier [Axis]: NPD Group Inc/The
Other Commitments [Line Items]
Unfunded commitments	0.9
Investment, Identifier [Axis]: Net Documents
Other Commitments [Line Items]
Unfunded commitments	2.9
Investment, Identifier [Axis]: New Era Technology Inc
Other Commitments [Line Items]
Unfunded commitments	2.1
Investment, Identifier [Axis]: Novotech Pty Ltd
Other Commitments [Line Items]
Unfunded commitments	5.6
Investment, Identifier [Axis]: Oxford Global Resources LLC 1
Other Commitments [Line Items]
Unfunded commitments	8.3
Investment, Identifier [Axis]: Oxford Global Resources LLC 2
Other Commitments [Line Items]
Unfunded commitments	4.1
Investment, Identifier [Axis]: PartsSource Inc 1
Other Commitments [Line Items]
Unfunded commitments	4.3
Investment, Identifier [Axis]: PartsSource Inc 2
Other Commitments [Line Items]
Unfunded commitments	22.7
Investment, Identifier [Axis]: RSC Insurance Brokerage Inc
Other Commitments [Line Items]
Unfunded commitments	7.6
Investment, Identifier [Axis]: Radwell International LLC/PA
Other Commitments [Line Items]
Unfunded commitments	6.9
Investment, Identifier [Axis]: Revere Superior Holdings Inc
Other Commitments [Line Items]
Unfunded commitments	1.7
Investment, Identifier [Axis]: Rise Baking Company
Other Commitments [Line Items]
Unfunded commitments	3.9
Investment, Identifier [Axis]: SAMBA Safety Inc
Other Commitments [Line Items]
Unfunded commitments	2.4
Investment, Identifier [Axis]: SavATree LLC 1
Other Commitments [Line Items]
Unfunded commitments	4.0
Investment, Identifier [Axis]: SavATree LLC 2
Other Commitments [Line Items]
Unfunded commitments	6.3
Investment, Identifier [Axis]: Source Code LLC
Other Commitments [Line Items]
Unfunded commitments	15.0
Investment, Identifier [Axis]: Spins LLC 1
Other Commitments [Line Items]
Unfunded commitments	16.5
Investment, Identifier [Axis]: Spins LLC 2
Other Commitments [Line Items]
Unfunded commitments	7.9
Investment, Identifier [Axis]: Summit Interconnect Inc
Other Commitments [Line Items]
Unfunded commitments	9.4
Investment, Identifier [Axis]: Sungard Availability Services Capital Inc
Other Commitments [Line Items]
Unfunded commitments	1.2
Investment, Identifier [Axis]: Sweeping Corp of America Inc
Other Commitments [Line Items]
Unfunded commitments	4.7
Investment, Identifier [Axis]: Time Manufacturing Co
Other Commitments [Line Items]
Unfunded commitments	14.8
Investment, Identifier [Axis]: Valeo Foods Group Ltd
Other Commitments [Line Items]
Unfunded commitments	3.1
Investment, Identifier [Axis]: Version1 Software Ltd
Other Commitments [Line Items]
Unfunded commitments	2.4
Investment, Identifier [Axis]: VetCor Professional Practices LLC 1
Other Commitments [Line Items]
Unfunded commitments	10.9
Investment, Identifier [Axis]: VetCor Professional Practices LLC 2
Other Commitments [Line Items]
Unfunded commitments	4.9
Investment, Identifier [Axis]: Wealth Enhancement Group LLC
Other Commitments [Line Items]
Unfunded commitments	3.3
Investment, Identifier [Axis]: Wealth Enhancement Group LLC 1
Other Commitments [Line Items]
Unfunded commitments	2.1
Investment, Identifier [Axis]: Woolpert Inc
Other Commitments [Line Items]
Unfunded commitments	3.7
Investment, Identifier [Axis]: Worldwise Inc 1
Other Commitments [Line Items]
Unfunded commitments	15.5
Investment, Identifier [Axis]: Worldwise Inc 2
Other Commitments [Line Items]
Unfunded commitments	6.8
Investment, Identifier [Axis]: Zendesk Inc 1
Other Commitments [Line Items]
Unfunded commitments	14.4
Investment, Identifier [Axis]: Zendesk Inc 2
Other Commitments [Line Items]
Unfunded commitments	6.0
Investment, Identifier [Axis]: iNova Pharmaceuticals (Australia) Pty Limited
Other Commitments [Line Items]
Unfunded commitments	$ 2.2