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 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Dec. 31, 2025
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]          
Beginning Balance $ 254,312 $ 279,704 $ 258,913 $ 281,541  
Total realized and unrealized gains (losses) included in net income 539 (1,005) 1,059 (763)  
Total realized and unrealized gains (losses) included in OCI (147) 3,828 (2,256) 7,191  
Purchases 18,650 90 26,149 2,876  
Sales 0 (17) 0 (17)  
Settlements (12,355) (4,108) (19,734) (12,436)  
Transfer into Level 3 6,618 0 8,618 100  
Transfer out of Level 3 (4,776) (22,382) (9,908) (22,382)  
Ending Balance 262,841 256,110 262,841 256,110  
Total gains (losses) attributable to assets still held included in net income 560 (1,001) 1,078 (759)  
Total gains (losses) attributable to assets still held included in OCI (166) 3,452 (2,296) 6,807  
Fixed maturity securities available-for-sale, at fair value (amortized cost of $6,258,735 and $6,081,997 as of June 30, 2026, and December 31, 2025, respectively) 6,161,975   6,161,975   $ 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 $6,258,735 and $6,081,997 as of June 30, 2026, and December 31, 2025, respectively) 223,468   223,468   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 $6,258,735 and $6,081,997 as of June 30, 2026, and December 31, 2025, respectively) 6,161,975   6,161,975   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 $6,258,735 and $6,081,997 as of June 30, 2026, and December 31, 2025, respectively) 223,468   223,468   $ 129,562
U.S. corporate          
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]          
Beginning Balance 189,390 225,970 197,721 222,786  
Total realized and unrealized gains (losses) included in net income 500 245 990 484  
Total realized and unrealized gains (losses) included in OCI (170) 3,081 (1,769) 6,248  
Purchases 3,000 0 3,000 0  
Sales 0 0 0 0  
Settlements (10,000) (4,000) (17,222) (4,222)  
Transfer into Level 3 0 0 0 0  
Transfer out of Level 3 0 (18,579) 0 (18,579)  
Ending Balance 182,720 206,717 182,720 206,717  
Total gains (losses) attributable to assets still held included in net income 522 245 1,012 484  
Total gains (losses) attributable to assets still held included in OCI (227) 2,758 (1,833) 5,925  
Non-U.S. corporate          
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]          
Beginning Balance 33,899 50,474 34,411 56,553  
Total realized and unrealized gains (losses) included in net income 18 (1,259) 36 (1,265)  
Total realized and unrealized gains (losses) included in OCI 5 724 (420) 956  
Purchases 4,000 90 4,000 1,890  
Sales 0 (17) 0 (17)  
Settlements (2,240) (106) (2,345) (8,211)  
Transfer into Level 3 0 0 0 0  
Transfer out of Level 3 0 (3,803) 0 (3,803)  
Ending Balance 35,682 46,103 35,682 46,103  
Total gains (losses) attributable to assets still held included in net income 18 (1,255) 36 (1,261)  
Total gains (losses) attributable to assets still held included in OCI 2 672 (423) 895  
Residential mortgage-backed          
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]          
Beginning Balance 446   483    
Total realized and unrealized gains (losses) included in net income 0   (1)    
Total realized and unrealized gains (losses) included in OCI (6)   (8)    
Purchases 5,400   5,400    
Sales 0      
Settlements (26)   (60)    
Transfer into Level 3 0   0    
Transfer out of Level 3 0   0    
Ending Balance 5,814   5,814    
Total gains (losses) attributable to assets still held included in net income 0   (1)    
Total gains (losses) attributable to assets still held included in OCI (6)   (8)    
Commercial mortgage-backed          
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]          
Beginning Balance 7,418   7,467    
Total realized and unrealized gains (losses) included in net income 1   2    
Total realized and unrealized gains (losses) included in OCI (6)   (56)    
Purchases 0   0    
Sales 0   0    
Settlements 0   0    
Transfer into Level 3 0   0    
Transfer out of Level 3 0   0    
Ending Balance 7,413   7,413    
Total gains (losses) attributable to assets still held included in net income 1   2    
Total gains (losses) attributable to assets still held included in OCI (6)   (56)    
Other asset-backed          
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]          
Beginning Balance 23,159 3,260 18,831 2,202  
Total realized and unrealized gains (losses) included in net income 20 9 32 18  
Total realized and unrealized gains (losses) included in OCI 30 23 (3) (13)  
Purchases 6,250 0 13,749 986  
Sales 0 0 0 0  
Settlements (89) (2) (107) (3)  
Transfer into Level 3 6,618 0 8,618 100  
Transfer out of Level 3 (4,776) 0 (9,908) 0  
Ending Balance 31,212 3,290 31,212 3,290  
Total gains (losses) attributable to assets still held included in net income 19 9 29 18  
Total gains (losses) attributable to assets still held included in OCI $ 71 $ 22 $ 24 $ (13)