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Debt - Summary of Interest Paid (Details) - USD ($) $ in Millions | 6 Months Ended
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Jun. 30, 2017 | Jun. 30, 2016
Debt Instrument [Line Items] |  |
Total interest payments | $ 32.2 | $ 28.7
Line of Credit | Revolving Credit Facility |  |
Debt Instrument [Line Items] |  |
Total interest payments | 0.5 | 0.0
FHLB Advance |  |
Debt Instrument [Line Items] |  |
Total interest payments | 1.5 | 0.9
5% Convertible Senior Notes due 2017 |  |
Debt Instrument [Line Items] |  |
Total interest payments | $ 3.6 | 6.9
Stated interest rate (in hundredths) | 5.00% |
2% Notes |  |
Debt Instrument [Line Items] |  |
Total interest payments | $ 2.1 | 5.0
Stated interest rate (in hundredths) | 2.00% |
5.75% Notes | 5.75% Notes |  |
Debt Instrument [Line Items] |  |
Total interest payments | $ 12.9 | 0.0
Stated interest rate (in hundredths) | 5.75% |
9% Debentures |  |
Debt Instrument [Line Items] |  |
Total interest payments | $ 11.6 | $ 15.9
Stated interest rate (in hundredths) | 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 Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + 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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