Debt - Summary of Debt Obligations (Details) - USD ($)	Jun. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Long-term debt, carrying value	$ 832,200,000	$ 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
Stated interest rate	1.91%
Senior Notes \| 5.75% Senior Notes Due 2023
Debt Instrument [Line Items]
Long-term debt, carrying value	$ 420,300,000	419,700,000
Stated interest rate	5.75%
Debt instrument, face amount	$ 425,000,000
9% Convertible Junior Subordinated Debentures
Debt Instrument [Line Items]
Long-term debt, carrying value	$ 256,900,000	$ 256,900,000
Stated interest rate	9.00%

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

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Contractual interest rate for funds borrowed, under the debt agreement.

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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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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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