Convertible Senior Notes - Schedule of Interest Expense Recognized (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Debt Instrument [Line Items]
Total	$ 11,337	$ 8,248	$ 20,015	$ 16,357
2022 Notes
Debt Instrument [Line Items]
Amortization of debt issuance cost	122	0	122	0
Amortization of debt discount	$ 2,388	$ 0	$ 2,388	$ 0
Effective interest rate of the liability component	4.75%	4.75%	4.75%	4.75%
2018 Notes
Debt Instrument [Line Items]
Amortization of debt issuance cost	$ 474	$ 442	$ 940	$ 877
Amortization of debt discount	$ 8,353	$ 7,806	$ 16,565	$ 15,480
Effective interest rate of the liability component	6.50%	6.50%	6.50%	6.50%