v3.26.3
Fair Value (Details) - USD ($)
$ in Thousands
Sep. 30, 2026
Dec. 31, 2025
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value $ 3,581,971 $ 3,439,002
Total 3,581,971 3,439,002
Total fixed maturities    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 3,157,925 3,238,543
U.S. government treasuries    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 350,678 797,834
U.S. states, territories and municipalities    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 9,239 12,960
Non-U.S. sovereign governments and supranationals    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 92,350 110,861
Corporate    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 1,829,404 1,584,144
Residential mortgage-backed securities - Agency    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 346,377 365,650
Residential mortgage-backed securities - Non-agency    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 96,434 32,545
Commercial mortgage-backed securities - Non-agency    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 84,482 94,698
Other asset-backed securities    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 348,961 239,851
Short-term investments    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 424,046 200,459
Level 1    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Total 0 0
Level 1 | Total fixed maturities    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 0 0
Level 1 | U.S. government treasuries    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 0 0
Level 1 | U.S. states, territories and municipalities    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 0 0
Level 1 | Non-U.S. sovereign governments and supranationals    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 0 0
Level 1 | Corporate    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 0 0
Level 1 | Residential mortgage-backed securities - Agency    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 0 0
Level 1 | Residential mortgage-backed securities - Non-agency    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 0 0
Level 1 | Commercial mortgage-backed securities - Non-agency    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 0 0
Level 1 | Other asset-backed securities    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 0 0
Level 1 | Short-term investments    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 0 0
Level 2    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Total 3,581,971 3,439,002
Level 2 | Total fixed maturities    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 3,157,925 3,238,543
Level 2 | U.S. government treasuries    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 350,678 797,834
Level 2 | U.S. states, territories and municipalities    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 9,239 12,960
Level 2 | Non-U.S. sovereign governments and supranationals    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 92,350 110,861
Level 2 | Corporate    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 1,829,404 1,584,144
Level 2 | Residential mortgage-backed securities - Agency    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 346,377 365,650
Level 2 | Residential mortgage-backed securities - Non-agency    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 96,434 32,545
Level 2 | Commercial mortgage-backed securities - Non-agency    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 84,482 94,698
Level 2 | Other asset-backed securities    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 348,961 239,851
Level 2 | Short-term investments    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 424,046 200,459
Level 3    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Total 0 0
Level 3 | Total fixed maturities    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 0 0
Level 3 | U.S. government treasuries    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 0 0
Level 3 | U.S. states, territories and municipalities    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 0 0
Level 3 | Non-U.S. sovereign governments and supranationals    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 0 0
Level 3 | Corporate    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 0 0
Level 3 | Residential mortgage-backed securities - Agency    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 0 0
Level 3 | Residential mortgage-backed securities - Non-agency    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 0 0
Level 3 | Commercial mortgage-backed securities - Non-agency    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 0 0
Level 3 | Other asset-backed securities    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value 0 0
Level 3 | Short-term investments    
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]    
Investments, at fair value $ 0 $ 0