Convertible Notes - Amortization expense, debt discount and debt issuance costs (Details) - Convertible Notes $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($)
Amortization expense for debt discount costs
April 1, 2020December 31, 2020	$ 6,708
January 1, 2021December 31, 2021	9,528
January 1, 2022December 31, 2022	10,241
January 1, 2023December 31, 2023	8,180
Total	34,657
Amortization expense for debt issuance costs
April 1, 2020December 31, 2020	681
January 1, 2021December 31, 2021	955
January 1, 2022December 31, 2022	1,015
January 1, 2023December 31, 2023	802
Total	$ 3,453