Convertible Senior Notes - Schedule of Interest Expense related to the Convertible Senior Notes (Details) - Convertible Senior Notes - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Series A Notes
Debt Instrument [Line Items]
Coupon interest	$ 1,150	$ 1,150	$ 2,300	$ 2,300
Amortization of convertible senior notes discounts and issuance costs	5,058	4,804	10,051	9,547
Total interest expense recognized	$ 6,208	$ 5,954	$ 12,351	$ 11,847
Effective interest rate on the liability component	6.40%	6.40%	6.40%	6.50%
Series B Notes
Debt Instrument [Line Items]
Coupon interest	$ 1,869	$ 1,869	$ 3,738	$ 3,738
Amortization of convertible senior notes discounts and issuance costs	4,283	4,085	8,515	8,122
Total interest expense recognized	$ 6,152	$ 5,954	$ 12,253	$ 11,860
Effective interest rate on the liability component	6.80%	6.90%	6.90%	7.00%