v3.26.3
Investments - Schedule of Fixed Maturity and Short-Term Investments (Details) - USD ($)
$ in Thousands
Sep. 30, 2026
Dec. 31, 2025
Debt Securities, Available-for-Sale [Line Items]    
Amortized Cost $ 3,691,050 $ 3,410,992
Gross Unrealized Gains 6,000 45,265
Gross Unrealized Losses (115,079) (17,255)
Investments, at fair value 3,581,971 3,439,002
Total fixed maturities    
Debt Securities, Available-for-Sale [Line Items]    
Amortized Cost 3,267,687 3,210,940
Gross Unrealized Gains 5,291 44,846
Gross Unrealized Losses (115,053) (17,243)
Investments, at fair value 3,157,925 3,238,543
U.S. government treasuries    
Debt Securities, Available-for-Sale [Line Items]    
Amortized Cost 365,667 795,780
Gross Unrealized Gains 0 4,782
Gross Unrealized Losses (14,989) (2,728)
Investments, at fair value 350,678 797,834
U.S. states, territories and municipalities    
Debt Securities, Available-for-Sale [Line Items]    
Amortized Cost 9,462 12,924
Gross Unrealized Gains 0 89
Gross Unrealized Losses (223) (53)
Investments, at fair value 9,239 12,960
Non-U.S. sovereign governments and supranationals    
Debt Securities, Available-for-Sale [Line Items]    
Amortized Cost 96,034 108,296
Gross Unrealized Gains 345 3,102
Gross Unrealized Losses (4,029) (537)
Investments, at fair value 92,350 110,861
Corporate    
Debt Securities, Available-for-Sale [Line Items]    
Amortized Cost 1,891,295 1,557,582
Gross Unrealized Gains 4,448 29,899
Gross Unrealized Losses (66,339) (3,337)
Investments, at fair value 1,829,404 1,584,144
Residential mortgage-backed securities - Agency    
Debt Securities, Available-for-Sale [Line Items]    
Amortized Cost 366,158 370,516
Gross Unrealized Gains 4 4,419
Gross Unrealized Losses (19,785) (9,285)
Investments, at fair value 346,377 365,650
Residential mortgage-backed securities - Non-agency    
Debt Securities, Available-for-Sale [Line Items]    
Amortized Cost 100,297 33,052
Gross Unrealized Gains 95 319
Gross Unrealized Losses (3,958) (826)
Investments, at fair value 96,434 32,545
Commercial mortgage-backed securities - Non-agency    
Debt Securities, Available-for-Sale [Line Items]    
Amortized Cost 87,238 94,223
Gross Unrealized Gains 3 835
Gross Unrealized Losses (2,759) (360)
Investments, at fair value 84,482 94,698
Other asset-backed securities    
Debt Securities, Available-for-Sale [Line Items]    
Amortized Cost 351,536 238,567
Gross Unrealized Gains 396 1,401
Gross Unrealized Losses (2,971) (117)
Investments, at fair value 348,961 239,851
Short-term investments    
Debt Securities, Available-for-Sale [Line Items]    
Amortized Cost 423,363 200,052
Gross Unrealized Gains 709 419
Gross Unrealized Losses (26) (12)
Investments, at fair value $ 424,046 $ 200,459