Convertible Debt - Schedule of Interest Expense Related to Notes (Details) - Convertible Debt - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
2017 Notes
Debt Instrument [Line Items]
Contractual interest expense	$ 404	$ 404
Interest cost related to amortization of the debt discount	5,212	4,909
Total interest expense	5,616	5,313
2018 Notes
Debt Instrument [Line Items]
Contractual interest expense	1,617	1,617
Interest cost related to amortization of the debt discount	6,887	6,344
Total interest expense	8,504	$ 7,961
2019 Notes
Debt Instrument [Line Items]
Contractual interest expense	2,319
Interest cost related to amortization of the debt discount	8,775
Total interest expense	$ 11,094