v3.26.3
Presentation of Financial Statements and Significant Accounting Policies - Narrative (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Jun. 04, 2026
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Dec. 31, 2025
Accounts, Notes, Loans and Financing Receivable [Line Items]            
Restricted cash   $ 873,032   $ 873,032   $ 628,651
Remaining liability   92,300   92,300   64,400
Total unamortized discount   30,100   30,100   12,800
Amortization and accretion of investment securities   6,400 $ 7,200 14,300 $ 16,400  
Change in estimate   6,200   6,200    
Long-lived asset, held and used, impairment loss   0 0 0 0  
Equity method investment, impairment   0 0 0 0  
Cash and cash equivalents   2,868,758 1,456,934 2,868,758 1,456,934 1,468,507
Net earned insurance premiums   315,849 $ 0 413,096 $ 0  
Amortized cost basis of financing receivables   522,100   522,100   560,300
Accrued interest on financing receivables   $ 50,500   $ 50,500   $ 48,200
Financing receivable threshold period past due   30 days   30 days    
Floreo            
Accounts, Notes, Loans and Financing Receivable [Line Items]            
Available borrowing amount   $ 365,000   $ 365,000    
Outstanding borrowings   276,000   276,000    
Bond Financing            
Accounts, Notes, Loans and Financing Receivable [Line Items]            
Maximum collateral required if conditions met       $ 100,000    
Debt instrument, loan-to-value ratio threshold       50.00%    
Asset Pledged as Collateral            
Accounts, Notes, Loans and Financing Receivable [Line Items]            
Restricted cash   259,500   $ 259,500    
Fixed maturity investments   30,200   30,200    
Fair Value Measured at Net Asset Value Per Share            
Accounts, Notes, Loans and Financing Receivable [Line Items]            
Other equity investments   4,900   4,900    
Vantage Group Holdings Ltd.            
Accounts, Notes, Loans and Financing Receivable [Line Items]            
Acquisition interest 100.00%          
Total consideration $ 2,100,000          
Value of business acquired (VOBA) $ 304,000          
Expected amortization, percentage, year one 90.00%          
Expected amortization, percentage, year two 9.00%          
Expected amortization, percentage, year three 1.00%          
Vantage Group Holdings Ltd. | Series A Preferred Stock | Private Placement            
Accounts, Notes, Loans and Financing Receivable [Line Items]            
Sale of stock, consideration received on transaction $ 1,000,000          
AdVantage Reinsurance Bermuda Ltd            
Accounts, Notes, Loans and Financing Receivable [Line Items]            
Net earned insurance premiums   3,400   4,400    
Fee and other income (losses)   18,900   $ 23,800    
AdVantage Reinsurance Bermuda Ltd | Minimum            
Accounts, Notes, Loans and Financing Receivable [Line Items]            
Reinsurance, premium, percentage assumed to net       2.20%    
AdVantage Reinsurance Bermuda Ltd | Maximum            
Accounts, Notes, Loans and Financing Receivable [Line Items]            
Reinsurance, premium, percentage assumed to net       2.50%    
AdVantage Reinsurance Bermuda Ltd | AV0002            
Accounts, Notes, Loans and Financing Receivable [Line Items]            
Variable interest entity ownership percentage       50.00%    
Cash and cash equivalents   $ 24,100   $ 24,100