Notes Payable - Interest Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Interest expense recognized related to the Notes
Amortization of debt issuance costs	$ 23,696	$ 14,053	$ 0
Convertible senior notes, 0.25%, due 2023
Interest expense recognized related to the Notes
Contractual interest expense	1,375	852
Amortization of debt issuance costs	1,858	1,102
Amortization of debt discount	21,838	12,951
Total interest expense related to the Notes	$ 25,071	$ 14,905