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Debt - Summary of Interest Paid (Details) - USD ($) $ in Millions | 9 Months Ended
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Sep. 30, 2018 | Sep. 30, 2017
Debt Instrument [Line Items] |  |
Total interest payments | $ 38.8 | $ 45.1
Line of Credit | Revolving Credit Facility |  |
Debt Instrument [Line Items] |  |
Total interest payments | 0.5 | 0.5
FHLB Advance |  |
Debt Instrument [Line Items] |  |
Total interest payments | 2.3 | 2.2
5% Convertible Senior Notes |  |
Debt Instrument [Line Items] |  |
Total interest payments | 0.0 | $ 3.6
Stated interest rate |  | 5.00%
2% Convertible Senior Notes |  |
Debt Instrument [Line Items] |  |
Total interest payments | 0.0 | $ 2.1
Stated interest rate |  | 2.00%
Senior Notes | 5.75% Senior Notes Due 2023 |  |
Debt Instrument [Line Items] |  |
Total interest payments | $ 24.4 | $ 25.1
Stated interest rate | 5.75% |
9% Convertible Junior Subordinated Debentures |  |
Debt Instrument [Line Items] |  |
Total interest payments | $ 11.6 | $ 11.6
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 of cash paid for interest. Includes, but is not limited to, payment to settle zero-coupon bond attributable to accreted interest of debt discount and debt instrument with insignificant coupon interest rate in relation to effective interest rate of borrowing attributable to accreted interest of debt discount. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4297-108586 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 25 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3536-108585 + Details
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