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Debt - Summary of Debt Obligations (Details) $ / shares in Units, $ in Millions | 1 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Apr. 30, 2017 | Jun. 30, 2017 USD ($) $ / shares | Dec. 31, 2016 USD ($)
Debt Instrument [Line Items] |  |  |
Long-term debt, par value |  | $ 836.9 | $ 1,189.5
Debt issuance costs |  | (7.0) | (10.8)
Long-term debt, carrying value |  | 829.9 | 1,178.7
FHLB Advance |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt, par value |  | 155.0 | 155.0
5% Convertible Senior Notes due 2017 |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt, par value |  | $ 0.0 | 145.0
Stated interest rate (in hundredths) |  | 5.00% |
2% Notes |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt, par value |  | $ 0.0 | 207.6
Stated interest rate (in hundredths) |  | 2.00% |
Conversion rate (in shares per $1,000 note) | 0.1438332 |  |
5.75% Notes | 5.75% Notes |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt, par value |  | $ 425.0 | 425.0
Stated interest rate (in hundredths) |  | 5.75% |
9% Debentures |  |  |
Debt Instrument [Line Items] |  |  |
Long-term debt, par value |  | $ 256.9 | $ 256.9
Stated interest rate (in hundredths) |  | 9.00% |
Conversion rate (in shares per $1,000 note) |  | 0.0740741 |
Convertible debt, conversion price (in dollars per share) | $ / shares |  | $ 13.50 |
Period preceding election to convert (in days) |  | 5 days |

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- Definition Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt. + 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)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: 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(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 3: 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 + Details
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- Definition Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.17) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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