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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Convertible Senior Notes due 2024
Debt Instrument [Line Items]
Coupon interest	$ 1,313	$ 1,313	$ 2,625	$ 2,625
Non-cash interest expense related to convertible senior notes	6,044	5,754	12,015	11,438
Total interest expense recognized	$ 7,357	$ 7,067	$ 14,640	$ 14,063
Effective interest rate on the liability component	6.00%	6.10%	6.10%	6.10%
Series A Notes
Debt Instrument [Line Items]
Coupon interest	$ 219	$ 300	$ 519	$ 599
Non-cash interest expense related to convertible senior notes	1,023	1,460	2,540	2,902
Total interest expense recognized	$ 1,242	$ 1,760	$ 3,059	$ 3,501
Effective interest rate on the liability component	4.20%	6.20%	5.20%	6.30%
Series B Notes
Debt Instrument [Line Items]
Coupon interest	$ 1,869	$ 1,869	$ 3,738	$ 3,717
Non-cash interest expense related to convertible senior notes	4,935	4,707	9,812	9,359
Total interest expense recognized	$ 6,804	$ 6,576	$ 13,550	$ 13,076
Effective interest rate on the liability component	6.60%	6.60%	6.60%	6.70%