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Debt - Summary of Debt Obligations (Details) - USD ($) | Mar. 31, 2019 | Dec. 31, 2018
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Debt Instrument [Line Items] |  |
Long-term debt, carrying value | $ 831,900,000 | $ 831,600,000
Federal Home Loan Bank Advances (FHLB) |  |
Debt Instrument [Line Items] |  |
Long-term debt, carrying value | $ 155,000,000 | 155,000,000
Stated interest rate | 1.91% |
Senior Notes | 5.75% Senior Notes Due 2023 |  |
Debt Instrument [Line Items] |  |
Long-term debt, carrying value | $ 420,000,000 | 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% |

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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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