v3.26.1
Segment Information - Revenues (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Segment Reporting [Line Items]        
Earned insurance premiums $ 384.6 $ 375.2   $ 770.2
Earned insurance premiums     $ 769.5  
Commission and fee revenues     103.6  
Commission and fee revenues 60.4 63.3   111.4
Product and service revenues 107.5 56.3 164.0 69.9
Total 552.5 494.8 1,037.1 951.5
United States        
Segment Reporting [Line Items]        
Earned insurance premiums 0.2 1.6   16.5
Earned insurance premiums     0.4  
Commission and fee revenues     96.2  
Commission and fee revenues 56.6 59.1   103.3
Product and service revenues 107.5 56.3 164.0 69.9
Total 164.3 117.0 260.6 189.7
United Kingdom        
Segment Reporting [Line Items]        
Earned insurance premiums 237.6 229.0   444.5
Earned insurance premiums     468.8  
Commission and fee revenues     0.0  
Commission and fee revenues 0.0 0.0   0.0
Product and service revenues 0.0 0.0 0.0 0.0
Total 237.6 229.0 468.8 444.5
Bermuda        
Segment Reporting [Line Items]        
Earned insurance premiums 146.8 144.6   309.2
Earned insurance premiums     300.3  
Commission and fee revenues     0.0  
Commission and fee revenues 0.0 0.0   0.0
Product and service revenues 0.0 0.0 0.0 0.0
Total 146.8 144.6 300.3 309.2
Other        
Segment Reporting [Line Items]        
Earned insurance premiums 0.0 0.0   0.0
Earned insurance premiums     0.0  
Commission and fee revenues     7.4  
Commission and fee revenues 3.8 4.2   8.1
Product and service revenues 0.0 0.0 0.0 0.0
Total $ 3.8 $ 4.2 $ 7.4 $ 8.1