Borrowings Convertible Debt (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($) $ / shares	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) $ / shares	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)	May 04, 2016 USD ($) $ / shares
Schedule of Convertible Debt [Line Items]
Document Fiscal Year Focus			2017
Debt Instrument, Convertible, Conversion Ratio			54.2741
Debt Instrument, Convertible, Conversion Price | $ / shares	$ 18.4250		$ 18.4250
Purchase of convertible note hedges			$ 0	$ (44,500,000)
Proceeds from Issuance of Warrants			0	39,100,000
Convertible Notes Due Twenty Twenty One [Member] | Convertible Debt
Schedule of Convertible Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						3.25%
Debt Instrument, Face Amount	$ 172,500,000		172,500,000		$ 172,500,000	$ 172,500,000
Debt Issuance Costs, Net	5,000,000		5,000,000
Debt Issuance Costs Attributable to the Equity Component			1,300,000
Deferred Tax Assets, Net	500,000		500,000
Debt Instrument, Unamortized Discount	(34,000,000)		(34,000,000)		(37,400,000)
Convertible notes payable	138,500,000		138,500,000		135,100,000
Convertible Debt, Current	(900,000)		(900,000)		(900,000)
Convertible Debt, Noncurrent	139,400,000		139,400,000		136,000,000
Debt Instrument, Convertible, Carrying Amount of Equity Component	29,900,000		29,900,000		$ 29,900,000
Debt Instrument, Fair Value Disclosure	202,400,000		202,400,000
Interest Expense, Debt, Excluding Amortization	1,400,000	$ 1,000,000	2,800,000	1,000,000
Amortization of Financing Costs	200,000	100,000	400,000	100,000
Amortization of Debt Discount (Premium)	1,500,000	900,000	2,900,000	900,000
Interest Expense, Debt	$ 3,100,000	2,000,000	$ 6,100,000	$ 2,000,000
Purchase of convertible note hedges		(44,500,000.00)
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares						$ 21.1050
Proceeds from Issuance of Warrants		$ 39,100,000