Convertible Senior Notes - Schedule of Interest Expense related to the Convertible Senior Notes (Details) - Convertible Senior Notes - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Convertible Senior Notes due 2024
Debt Instrument [Line Items]
Coupon interest	$ 1,313	$ 1,313	$ 3,938	$ 3,145
Non-cash interest expense related to convertible senior notes	6,119	5,825	18,133	17,264
Total interest expense recognized	$ 7,432	$ 7,138	$ 22,071	$ 20,409
Effective interest rate on the liability component	6.00%	6.10%	6.10%	6.10%
Series A Notes
Debt Instrument [Line Items]
Coupon interest	$ 59	$ 300	$ 577	$ 2,537
Non-cash interest expense related to convertible senior notes	0	1,460	2,540	11,785
Total interest expense recognized	$ 59	$ 1,760	$ 3,117	$ 14,322
Effective interest rate on the liability component	1.00%	6.20%	3.50%	6.30%
Series B Notes
Debt Instrument [Line Items]
Coupon interest	$ 1,869	$ 1,869	$ 5,606	$ 5,585
Non-cash interest expense related to convertible senior notes	4,994	4,763	14,806	14,123
Total interest expense recognized	$ 6,863	$ 6,632	$ 20,412	$ 19,708
Effective interest rate on the liability component	6.50%	6.60%	6.60%	6.70%