v3.26.1
Related-Party Transactions - Narrative (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jan. 01, 2025
Jul. 01, 2022
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Dec. 31, 2025
Related Party Transaction [Line Items]              
Current capitalization     $ 9,833,239   $ 9,833,239   $ 9,700,818
Written premiums, Ceded     713,766 $ 626,330 1,325,186 $ 1,176,966  
Ceded commissions and brokerage     156,093 135,919 309,041 275,523  
Due to reinsurers     646,261   646,261   615,781
Written premiums, assumed     $ 332,191 366,985 $ 646,771 740,031  
Mitsui Sumitomo Insurance Co., Ltd. | Common stocks              
Related Party Transaction [Line Items]              
Percent of stock held by related party     15.80%   15.80%    
Nonrelated Party | Lifson Re              
Related Party Transaction [Line Items]              
Current capitalization     $ 418,000   $ 418,000    
Nonrelated Party | Lifson Re              
Related Party Transaction [Line Items]              
Due to reinsurers     135,367   135,367   $ 118,788
Nonrelated Party | Lifson Re | Management And Performance Fees              
Related Party Transaction [Line Items]              
Ceded commissions earned         5,000 3,000  
Nonrelated Party | Reinsurer Concentration Risk | Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments | Lifson Re              
Related Party Transaction [Line Items]              
Concentration risk, percentage 32.50% 30.00%          
Written premiums, Ceded     148,571 140,363 267,088 246,500  
Ceded commissions and brokerage     34,442 $ 35,656 68,367 $ 66,080  
Nonrelated Party | Reinsurer Concentration Risk | Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments | Mitsui Sumitomo Insurance Co., Ltd.              
Related Party Transaction [Line Items]              
Written premiums, Ceded     19,000   34,000    
Ceded commissions and brokerage     4,000   7,000    
Due from reinsurers     69,000   69,000    
Due to reinsurers     13,000   13,000    
Written premiums, assumed     10,000   15,000    
Assumed premiums receivable     8,000   8,000    
Assumed premiums, reinsurance payable     $ 8,000   $ 8,000