Debt - Liability Component and Interest Expense (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended		3 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 Senior Convertible Notes	Aug. 31, 2013 Senior Convertible Notes
Liability Component
Principal amount					$ 150,000
Unamortized debt discount					(31,042)
Net carrying amount	1,161		1,161		118,958	111,500
Interest Expense
Contractual interest expense at 1.5% per annum					1,688
Amortization of debt issuance costs					470
Accretion of debt discount					5,043
Total	$ 2,495	$ 1,272	$ 7,356	$ 1,376	$ 7,201