v3.26.1
Fair value - Summary of Fair Value Assets Measured on Recurring Basis, Significant Unobservable Input (Details)
$ in Thousands
Mar. 31, 2026
USD ($)
Dec. 31, 2025
USD ($)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value $ 6,133,789 $ 6,050,542
U.S. corporate    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 2,823,996 2,810,727
Non-U.S. corporate    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 816,324 783,056
Residential mortgage-backed    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 341,484 349,333
Commercial mortgage-backed    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 198,632 129,562
Fair value, recurring    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 6,133,789 6,050,542
Fair value, recurring | U.S. corporate    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 2,823,996 2,810,727
Fair value, recurring | Non-U.S. corporate    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 816,324 783,056
Fair value, recurring | Residential mortgage-backed    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 341,484 349,333
Fair value, recurring | Commercial mortgage-backed    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value $ 198,632 129,562
Level 3  | U.S. corporate | Internal models | Credit spreads | Minimum    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fixed maturity securities, measurement input (in basis points) 0.0014  
Level 3  | U.S. corporate | Internal models | Credit spreads | Maximum    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fixed maturity securities, measurement input (in basis points) 0.0206  
Level 3  | U.S. corporate | Internal models | Credit spreads | Weighted average    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fixed maturity securities, measurement input (in basis points) 0.0098  
Level 3  | Non-U.S. corporate | Internal models | Credit spreads | Minimum    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fixed maturity securities, measurement input (in basis points) 0.0091  
Level 3  | Non-U.S. corporate | Internal models | Credit spreads | Maximum    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fixed maturity securities, measurement input (in basis points) 0.0143  
Level 3  | Non-U.S. corporate | Internal models | Credit spreads | Weighted average    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fixed maturity securities, measurement input (in basis points) 0.0106  
Level 3  | Fair value, recurring    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value $ 254,312 258,913
Level 3  | Fair value, recurring | Internal models    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 228,700  
Level 3  | Fair value, recurring | U.S. corporate    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 189,390 197,721
Level 3  | Fair value, recurring | U.S. corporate | Internal models    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 189,390  
Level 3  | Fair value, recurring | Non-U.S. corporate    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 33,899 34,411
Level 3  | Fair value, recurring | Non-U.S. corporate | Internal models    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 29,812  
Level 3  | Fair value, recurring | Residential mortgage-backed    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 446 483
Level 3  | Fair value, recurring | Commercial mortgage-backed    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value $ 7,418 $ 7,467