v3.25.2
Segment Information - Revenues (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Segment Reporting Information [Line Items]        
Earned insurance premiums $ 375.2 $ 343.9 $ 770.2 $ 662.9
Commission and fee revenues 63.3 36.1 111.4 61.6
Other revenues 56.3 13.9 69.9 28.2
Total 494.8 393.9 951.5 752.7
UNITED STATES        
Segment Reporting Information [Line Items]        
Earned insurance premiums 1.6 1.5 16.5 2.8
Commission and fee revenues 59.1 32.7 103.3 54.6
Other revenues 56.3 13.9 69.9 28.2
Total 117.0 48.1 189.7 85.6
UNITED KINGDOM        
Segment Reporting Information [Line Items]        
Earned insurance premiums 229.0 193.7 444.5 371.1
Commission and fee revenues 0.0 0.0 0.0 0.0
Other revenues 0.0 0.0 0.0 0.0
Total 229.0 193.7 444.5 371.1
BERMUDA        
Segment Reporting Information [Line Items]        
Earned insurance premiums 144.6 148.7 309.2 289.0
Commission and fee revenues 0.0 0.0 0.0 0.0
Other revenues 0.0 0.0 0.0 0.0
Total 144.6 148.7 309.2 289.0
Other country        
Segment Reporting Information [Line Items]        
Earned insurance premiums 0.0 0.0 0.0 0.0
Commission and fee revenues 4.2 3.4 8.1 7.0
Other revenues 0.0 0.0 0.0 0.0
Total $ 4.2 $ 3.4 $ 8.1 $ 7.0