v3.26.1
Fair value - Narrative (Details) - USD ($)
$ in Thousands
Jun. 30, 2026
Dec. 31, 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities $ 6,161,975 $ 6,050,542
U.S. corporate    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 2,776,874 2,810,727
Non-U.S. corporate    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 849,991 783,056
Fair value, recurring    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 6,161,975 6,050,542
Liabilities, fair value 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 2,776,874 2,810,727
Fair value, recurring | Non-U.S. corporate    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 849,991 783,056
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 286,142 257,307
Level 1 | Fair value, recurring    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 0 0
Level 1 | Fair value, recurring | U.S. corporate    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 0 0
Level 1 | Fair value, recurring | Non-U.S. corporate    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 0 0
Level 1 | 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 0 0
Level 2 | Fair value, recurring    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities $ 5,899,134 5,791,629
Percentage of portfolio priced using third-party pricing services 90.00%  
Level 2 | Fair value, recurring | U.S. corporate    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities $ 2,594,154 2,613,006
Level 2 | Fair value, recurring | U.S. corporate | Internal models    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 227,700  
Level 2 | Fair value, recurring | U.S. corporate | Pricing Services    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 2,366,458  
Level 2 | Fair value, recurring | Non-U.S. corporate    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 814,309 748,645
Level 2 | Fair value, recurring | Non-U.S. corporate | Internal models    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 85,600  
Level 2 | Fair value, recurring | Non-U.S. corporate | Pricing Services    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 728,719  
Level 2 | 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 286,142 257,307
Level 2 | Fair value, recurring | U.S. government, agencies and GSEs | Pricing Services    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 286,142  
Level 3  | Fair value, recurring    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 262,841 258,913
Level 3  | Fair value, recurring | Internal models    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 227,000  
Level 3  | Fair value, recurring | Valuation technique, broker quotes    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 30,900  
Level 3  | Fair value, recurring | U.S. corporate    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 182,720 197,721
Level 3  | Fair value, recurring | U.S. corporate | Internal models    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 182,720  
Level 3  | Fair value, recurring | Non-U.S. corporate    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 35,682 34,411
Level 3  | Fair value, recurring | Non-U.S. corporate | Internal models    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 31,576  
Level 3  | 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 0 $ 0
Level 3  | Fair value, recurring | U.S. government, agencies and GSEs | Pricing Services    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities $ 4,900