v3.25.2
Investment Securities - Investment Holdings (Details) - USD ($)
$ in Millions
 6 Months Ended 12 Months Ended
Jun. 30, 2025
Dec. 31, 2024
U.S. Government and agency obligations    
Debt and Equity Securities, FV-NI [Line Items]    
Cost or Amortized Cost $ 480.8 $ 461.8
Gross Unrealized Gains 2.0 1.1
Gross Unrealized Losses (0.3) (0.8)
Net Foreign Currency Gains (Losses) 0.0 0.0
Carrying Value 482.5 462.1
Debt securities issued by corporations    
Debt and Equity Securities, FV-NI [Line Items]    
Cost or Amortized Cost 1,419.4 1,444.5
Gross Unrealized Gains 11.1 4.6
Gross Unrealized Losses (17.0) (31.4)
Net Foreign Currency Gains (Losses) (0.3) (3.5)
Carrying Value 1,413.2 1,414.2
Municipal obligations    
Debt and Equity Securities, FV-NI [Line Items]    
Cost or Amortized Cost 3.2 3.2
Gross Unrealized Gains 0.0 0.0
Gross Unrealized Losses 0.0 0.0
Net Foreign Currency Gains (Losses) 0.0 0.0
Carrying Value 3.2 3.2
Mortgage and asset-backed securities    
Debt and Equity Securities, FV-NI [Line Items]    
Cost or Amortized Cost 421.9 400.2
Gross Unrealized Gains 1.5 0.2
Gross Unrealized Losses (20.9) (26.5)
Net Foreign Currency Gains (Losses) 0.0 0.0
Carrying Value 402.5 373.9
Collateralized loan obligations    
Debt and Equity Securities, FV-NI [Line Items]    
Cost or Amortized Cost 303.0 237.3
Gross Unrealized Gains 0.9 1.2
Gross Unrealized Losses (0.1) (0.2)
Net Foreign Currency Gains (Losses) 3.0 (1.6)
Carrying Value 306.8 236.7
Foreign government and agency obligations    
Debt and Equity Securities, FV-NI [Line Items]    
Cost or Amortized Cost 26.0 22.2
Gross Unrealized Gains 0.2 0.0
Gross Unrealized Losses 0.0 (0.1)
Net Foreign Currency Gains (Losses) 1.5 (0.6)
Carrying Value 27.7 21.5
Fixed maturity investments    
Debt and Equity Securities, FV-NI [Line Items]    
Cost or Amortized Cost 2,654.3 2,569.2
Gross Unrealized Gains 15.7 7.1
Gross Unrealized Losses (38.3) (59.0)
Net Foreign Currency Gains (Losses) 4.2 (5.7)
Carrying Value $ 2,635.9 $ 2,511.6