Debt - Summary of Debt Obligations (Details) - USD ($)	Mar. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Long-term debt, carrying value	$ 935,300,000	$ 1,146,700,000
Federal Home Loan Bank Advances (FHLB)
Debt Instrument [Line Items]
Long-term debt, carrying value	$ 0	155,000,000.0
Stated interest rate	1.91%
Senior Notes | 5.75% Senior Notes Due 2023
Debt Instrument [Line Items]
Long-term debt, carrying value	$ 241,400,000	241,300,000
Stated interest rate	5.75%
Debt instrument, face amount	$ 242,300,000
Senior Notes | 5.25% Senior Notes Due 2028
Debt Instrument [Line Items]
Long-term debt, carrying value	$ 640,600,000	640,200,000
Stated interest rate	5.25%
Debt instrument, face amount	$ 650,000,000
9% Convertible Junior Subordinated Debentures
Debt Instrument [Line Items]
Long-term debt, carrying value	$ 53,300,000	$ 110,200,000
Stated interest rate	9.00%