v3.25.2
Fair value - Narrative (Details) - USD ($)
$ in Thousands
Jun. 30, 2025
Dec. 31, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities $ 5,896,818 $ 5,624,773
U.S. corporate    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 2,851,475 2,825,679
Non-U.S. corporate    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 783,184 772,624
Fair value, recurring    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 5,896,818 5,624,773
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 2,851,475 2,825,679
Fair value, recurring | Non-U.S. corporate    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 783,184 772,624
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 2 | Fair value, recurring    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities $ 5,640,708 5,343,232
Percentage of portfolio priced using third-party pricing services 91.00%  
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 $ 2,644,758 2,602,893
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 217,600  
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 737,081 716,071
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 77,400  
Level 3  | Fair value, recurring    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 256,110 281,541
Level 3  | Fair value, recurring | Internal models    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 241,900  
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 14,200  
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 206,717 222,786
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 206,717  
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 46,103 $ 56,553
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 $ 35,164