Income tax - Schedule of Tax Character of Distributions (Details) - USD ($) $ in Millions  | 
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2024  | 
Dec. 31, 2023  | 
Dec. 31, 2022  | 
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| Income Tax Disclosure [Abstract] | |||
| Ordinary income | $ 286.1 | $ 275.5 | $ 203.7 | 
| Long-term capital gains | $ 23.4 | $ 0.0 | $ 43.1 | 
| X | ||||||||||
- References No definition available. 
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| X | ||||||||||
- Definition Amount of dividend distribution by investment company from long-term capital gain. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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| X | ||||||||||
- Definition Amount of dividend distribution by investment company from ordinary income. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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