Debt Summary of Obligations (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Long-term debt, carrying value	$ 832,700,000	$ 831,600,000
Federal Home Loan Bank Advances (FHLB)
Debt Instrument [Line Items]
Long-term debt, carrying value	155,000,000.0	155,000,000.0
Senior Notes \| 5.75% Senior Notes due 2023
Debt Instrument [Line Items]
Long-term debt, carrying value	$ 420,900,000	419,700,000
Stated interest rate (in hundredths)	5.75%
Debt instrument, face amount	$ 425,000,000
Convertible Junior Subordinated Debentures, at 9% per annum, Due 2063
Debt Instrument [Line Items]
Long-term debt, carrying value	$ 256,900,000	$ 256,900,000
Stated interest rate (in hundredths)	9.00%

Face (par) amount of debt instrument at time of issuance.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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