v3.26.1
Fair value - Schedule of Additional Information about Fair Value Assets Measured on Recurring Basis, Unobservable Input Reconciliation (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Dec. 31, 2025
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]      
Beginning Balance $ 258,913 $ 281,541  
Total realized and unrealized gains (losses) included in net income 520 242  
Total realized and unrealized gains (losses) included in OCI (2,109) 3,363  
Purchases 7,499 2,786  
Sales 0 0  
Settlements (7,379) (8,328)  
Transfer into Level 3 2,000 100  
Transfer out of Level 3 (5,132) 0  
Ending Balance 254,312 279,704  
Total gains (losses) attributable to assets still held included in net income 518 242  
Total gains (losses) attributable to assets still held included in OCI (2,130) 3,355  
Fixed maturity securities available-for-sale, at fair value (amortized cost of $6,229,802 and $6,081,997 as of March 31, 2026, and December 31, 2025, respectively) 6,133,789   $ 6,050,542
Commercial mortgage-backed      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]      
Fixed maturity securities available-for-sale, at fair value (amortized cost of $6,229,802 and $6,081,997 as of March 31, 2026, and December 31, 2025, respectively) 198,632   129,562
Fair value, recurring      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]      
Fixed maturity securities available-for-sale, at fair value (amortized cost of $6,229,802 and $6,081,997 as of March 31, 2026, and December 31, 2025, respectively) 6,133,789   6,050,542
Fair value, recurring | Commercial mortgage-backed      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]      
Fixed maturity securities available-for-sale, at fair value (amortized cost of $6,229,802 and $6,081,997 as of March 31, 2026, and December 31, 2025, respectively) 198,632   $ 129,562
U.S. corporate      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]      
Beginning Balance 197,721 222,786  
Total realized and unrealized gains (losses) included in net income 490 239  
Total realized and unrealized gains (losses) included in OCI (1,599) 3,167  
Purchases 0 0  
Sales 0 0  
Settlements (7,222) (222)  
Transfer into Level 3 0 0  
Transfer out of Level 3 0 0  
Ending Balance 189,390 225,970  
Total gains (losses) attributable to assets still held included in net income 490 239  
Total gains (losses) attributable to assets still held included in OCI (1,606) 3,167  
Non-U.S. corporate      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]      
Beginning Balance 34,411 56,553  
Total realized and unrealized gains (losses) included in net income 18 (6)  
Total realized and unrealized gains (losses) included in OCI (425) 232  
Purchases 0 1,800  
Sales 0 0  
Settlements (105) (8,105)  
Transfer into Level 3 0 0  
Transfer out of Level 3 0 0  
Ending Balance 33,899 50,474  
Total gains (losses) attributable to assets still held included in net income 18 (6)  
Total gains (losses) attributable to assets still held included in OCI (425) 223  
Residential mortgage-backed      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]      
Beginning Balance 483    
Total realized and unrealized gains (losses) included in net income (1)    
Total realized and unrealized gains (losses) included in OCI (2)    
Purchases 0    
Sales 0    
Settlements (34)    
Transfer into Level 3 0    
Transfer out of Level 3 0    
Ending Balance 446    
Total gains (losses) attributable to assets still held included in net income (1)    
Total gains (losses) attributable to assets still held included in OCI (2)    
Commercial mortgage-backed      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]      
Beginning Balance 7,467    
Total realized and unrealized gains (losses) included in net income 1    
Total realized and unrealized gains (losses) included in OCI (50)    
Purchases 0    
Sales 0    
Settlements 0    
Transfer into Level 3 0    
Transfer out of Level 3 0    
Ending Balance 7,418    
Total gains (losses) attributable to assets still held included in net income 1    
Total gains (losses) attributable to assets still held included in OCI (50)    
Other asset-backed      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]      
Beginning Balance 18,831 2,202  
Total realized and unrealized gains (losses) included in net income 12 9  
Total realized and unrealized gains (losses) included in OCI (33) (36)  
Purchases 7,499 986  
Sales 0 0  
Settlements (18) (1)  
Transfer into Level 3 2,000 100  
Transfer out of Level 3 (5,132) 0  
Ending Balance 23,159 3,260  
Total gains (losses) attributable to assets still held included in net income 10 9  
Total gains (losses) attributable to assets still held included in OCI $ (47) $ (35)