v3.26.1
Fair value - Narrative (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
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
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
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 2,823,996 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 816,324 783,056
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 268,722 257,307
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 $ 5,879,477 5,791,629
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 $ 2,634,606 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 230,400  
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 2,404,183  
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 782,425 748,645
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 82,500  
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 699,923  
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 268,722 257,307
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 268,722  
Level 3  | Fair value, recurring    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 254,312 258,913
Level 3  | Fair value, recurring | Internal models    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total fixed maturity securities 228,700  
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 22,600  
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 189,390 197,721
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 189,390  
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 33,899 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 29,812  
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 $ 3,000