v3.26.3
Reserves for Claims and Claim Expenses (Details) - USD ($)
$ in Thousands
 9 Months Ended
Sep. 30, 2026
Dec. 31, 2025
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]    
Reserves for claims and claim expenses, beginning balance $ 0  
Reinsurance recoverable on unpaid losses, beginning balance 0  
Net reserve for claims and claim expenses, beginning balance 0  
Acquired net reserve for claims and claim expenses 1,535,414  
Net losses incurred during the period related to:    
Current period 256,879  
Prior period (1,118)  
Total net losses incurred 255,761  
Net losses paid during the period related to:    
Current period (23,007)  
Prior period (101,421)  
Total net losses paid (124,428)  
Foreign exchange (gains) losses (212)  
Net reserve for claims and claim expenses, ending balance 1,666,535  
Reinsurance recoverable on unpaid losses, ending balance 595,771  
Reserves for claims and claim expenses, ending balance 2,262,306  
Reinsurance recoverable on paid and unpaid losses 630,049 $ 0
Prior period reclassification adjustment (4,000)  
Reinsurance recoverable for paid claims and claims adjustments 34,300  
Vantage Group Holdings Ltd.    
Net losses paid during the period related to:    
Reinsurance recoverable on unpaid losses, ending balance 554,800  
Reserves for claims and claim expenses, ending balance 2,100,000  
Reinsurance recoverable on paid and unpaid losses 44,300  
Business combination, acquisition-related cost, expense $ 2,900