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Investments in debt and equity securities - Additional Information (Details)
$ in Millions
Mar. 31, 2025
USD ($)
investment
Dec. 31, 2024
USD ($)
Investments, Debt and Equity Securities [Abstract]    
Net unrealized investment gains on equity securities held | $ $ 25.8 $ 23.2
Number of investments in an unrealized loss position 254  
Number of investments in an unrealized loss positions for more than 12 months 204