v3.26.1
Fair value - Schedule of Fair Value Assets Measured on Recurring Basis (Details) - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities $ 6,133,789 $ 6,050,542
State and political subdivisions    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 469,832 478,972
Non-U.S. government    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 179,543 185,462
U.S. corporate    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 2,823,996 2,810,727
Non-U.S. corporate    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 816,324 783,056
Residential mortgage-backed    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 341,484 349,333
Commercial mortgage-backed    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 198,632 129,562
Other asset-backed    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 1,035,256 1,056,123
Fair value, recurring    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 6,133,789 6,050,542
Fair value, recurring | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 0 0
Fair value, recurring | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 5,879,477 5,791,629
Fair value, recurring | Level 3     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 254,312 258,913
Fair value, recurring | U.S. government, agencies and GSEs    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 268,722 257,307
Fair value, recurring | U.S. government, agencies and GSEs | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 0 0
Fair value, recurring | U.S. government, agencies and GSEs | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 268,722 257,307
Fair value, recurring | U.S. government, agencies and GSEs | Level 3     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 0 0
Fair value, recurring | State and political subdivisions    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 469,832 478,972
Fair value, recurring | State and political subdivisions | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 0 0
Fair value, recurring | State and political subdivisions | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 469,832 478,972
Fair value, recurring | State and political subdivisions | Level 3     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 0 0
Fair value, recurring | Non-U.S. government    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 179,543 185,462
Fair value, recurring | Non-U.S. government | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 0 0
Fair value, recurring | Non-U.S. government | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 179,543 185,462
Fair value, recurring | Non-U.S. government | Level 3     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 0 0
Fair value, recurring | U.S. corporate    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 2,823,996 2,810,727
Fair value, recurring | U.S. corporate | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 0 0
Fair value, recurring | U.S. corporate | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 2,634,606 2,613,006
Fair value, recurring | U.S. corporate | Level 3     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 189,390 197,721
Fair value, recurring | Non-U.S. corporate    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 816,324 783,056
Fair value, recurring | Non-U.S. corporate | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 0 0
Fair value, recurring | Non-U.S. corporate | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 782,425 748,645
Fair value, recurring | Non-U.S. corporate | Level 3     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 33,899 34,411
Fair value, recurring | Residential mortgage-backed    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 341,484 349,333
Fair value, recurring | Residential mortgage-backed | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 0 0
Fair value, recurring | Residential mortgage-backed | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 341,038 348,850
Fair value, recurring | Residential mortgage-backed | Level 3     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 446 483
Fair value, recurring | Commercial mortgage-backed    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 198,632 129,562
Fair value, recurring | Commercial mortgage-backed | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 0 0
Fair value, recurring | Commercial mortgage-backed | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 191,214 122,095
Fair value, recurring | Commercial mortgage-backed | Level 3     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 7,418 7,467
Fair value, recurring | Other asset-backed    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 1,035,256 1,056,123
Fair value, recurring | Other asset-backed | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 0 0
Fair value, recurring | Other asset-backed | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 1,012,097 1,037,292
Fair value, recurring | Other asset-backed | Level 3     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities $ 23,159 $ 18,831