Debt - Summary of Obligations (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Long-term debt, carrying value	$ 1,146.7	$ 1,243.2
Federal Home Loan Bank Advances (FHLB)
Debt Instrument [Line Items]
Long-term debt, carrying value	155.0	155.0
Senior Notes | 5.75% Senior Notes due 2023
Debt Instrument [Line Items]
Long-term debt, carrying value	241.3	240.6
Senior Notes | 5.25% Senior Notes due 2028
Debt Instrument [Line Items]
Long-term debt, carrying value	640.2	638.8
Convertible Junior Subordinated Debentures, at 9% per annum, Due 2063
Debt Instrument [Line Items]
Long-term debt, carrying value	$ 110.2	$ 208.8