Borrowings Convertible Debt (Details) - Convertible Debt - Convertible Notes Due Twenty Twenty One
$ / shares in Units, $ in Millions |
3 Months Ended |
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Mar. 31, 2018
USD ($)
$ / shares
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Mar. 31, 2017
USD ($)
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Jun. 30, 2016
USD ($)
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Dec. 31, 2017
USD ($)
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May 04, 2016
USD ($)
$ / shares
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| Schedule of Convertible Debt |
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| Debt Instrument, Interest Rate, Stated Percentage |
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3.25%
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| Debt Instrument, Convertible, Conversion Ratio |
54.2741
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| Debt Instrument, Convertible, Conversion Price | $ / shares |
$ 18.4250
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| Debt Issuance Costs, Net |
$ 5.0
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| Debt Issuance Costs Attributable to the Equity Component |
1.3
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| Deferred Tax Assets, Net |
0.5
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| Debt Instrument, Face Amount |
172.5
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$ 172.5
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$ 172.5
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| Debt Instrument, Unamortized Discount |
28.9
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30.6
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| Convertible Notes Payable |
143.6
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141.9
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| Convertible Notes Payable, Current |
0.0
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0.0
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| Convertible Notes Payable, Noncurrent |
143.6
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141.9
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| Debt Instrument, Convertible, Carrying Amount of Equity Component |
29.9
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$ 29.9
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| Debt Instrument, Fair Value Disclosure |
179.5
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| Interest Expense, Debt, Excluding Amortization |
1.4
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$ 1.4
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| Amortization of Debt Issuance Costs |
0.2
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0.2
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| Amortization of Debt Discount (Premium) |
1.5
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1.4
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| Interest Expense, Debt |
$ 3.1
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$ 3.0
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| Payments for Hedge, Financing Activities |
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$ 44.5
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| Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares |
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$ 21.1050
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| Proceeds from issuance of warrants |
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$ 39.1
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