Debt - Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Debt Instrument [Line Items]
Total interest expense	$ 1,338	$ 2,444
Senior Notes
Debt Instrument [Line Items]
Contractual interest expense	139	629
Amortization of debt discount	0	1,390
Amortization of debt issuance costs	789	186
Total interest expense	928	2,205
1.75% Convertible Senior Notes due 2023 | Senior Notes
Debt Instrument [Line Items]
Contractual interest expense	104	629
Amortization of debt discount	0	1,390
Amortization of debt issuance costs	72	186
Total interest expense	176	2,205
0% Convertible Senior Notes due 2025 | Senior Notes
Debt Instrument [Line Items]
Contractual interest expense	0	0
Amortization of debt discount	0	0
Amortization of debt issuance costs	690	0
Total interest expense	690	0
0.5% Convertible Senior Notes Due 2027 | Senior Notes
Debt Instrument [Line Items]
Contractual interest expense	35	0
Amortization of debt discount	0	0
Amortization of debt issuance costs	27	0
Total interest expense	$ 62	$ 0