v3.26.3
Reinsurance (Effect Of Reinsurance And Retrocessional Reinsurance On Premiums Written And Earned) (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Effects of Reinsurance [Line Items]        
Direct premiums written $ 3,410,151 $ 3,124,486 $ 9,825,591 $ 9,270,669
Direct premiums earned 3,322,039 3,118,899 9,464,741 9,096,408
Assumed premiums written 580,234 734,407 2,521,990 3,950,945
Assumed premiums earned 1,166,251 1,565,605 2,695,497 3,016,157
Ceded premiums written (1,750,297) (1,620,697) (6,138,791) (6,429,776)
Ceded premiums earned (2,212,782) (2,478,731) (5,764,066) (5,675,727)
Net premiums written 2,240,088 2,238,196 6,208,790 6,791,838
Net premiums earned 2,275,508 2,205,773 6,396,172 6,436,838
Underwriting        
Effects of Reinsurance [Line Items]        
Direct premiums written 2,372,205 2,420,107 6,724,591 6,970,879
Direct premiums earned 2,367,480 2,275,753 6,918,925 6,681,520
Assumed premiums written 200,863 382,313 604,775 1,583,225
Assumed premiums earned 334,950 453,405 1,000,231 1,342,521
Ceded premiums written (333,095) (563,681) (1,120,859) (1,761,973)
Ceded premiums earned (428,557) (522,939) (1,524,734) (1,587,018)
Net premiums written 2,239,973 2,238,739 6,208,507 6,792,131
Net premiums earned 2,273,873 2,206,219 6,394,422 6,437,023
Fronting        
Effects of Reinsurance [Line Items]        
Direct premiums written 1,037,946 704,379 3,101,000 2,299,790
Direct premiums earned 954,559 843,146 2,545,816 2,414,888
Assumed premiums written 379,371 352,094 1,917,215 2,367,720
Assumed premiums earned 831,301 1,112,200 1,695,266 1,673,636
Ceded premiums written (1,417,202) (1,057,016) (5,017,932) (4,667,803)
Ceded premiums earned (1,784,225) (1,955,792) (4,239,332) (4,088,709)
Net premiums written 115 (543) 283 (293)
Net premiums earned $ 1,635 $ (446) $ 1,750 $ (185)