Debt Obligations - Schedule of Interest Expense (Details) - 1.75% Convertible Senior Notes Due 2022 - Senior Notes - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Nov. 30, 2017	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Line of Credit Facility [Line Items]
Contractual interest expense		$ 875	$ 875	$ 2,625	$ 2,625
Amortization of debt discount		2,540	2,396	7,510	7,086
Amortization of debt issuance costs	$ 4,600	231	230	693	690
Total interest expense related to the Notes		$ 3,646	$ 3,501	$ 10,828	$ 10,401