Debt - Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Debt Instrument [Line Items]
Total interest expense	$ 3,672	$ 2,522	$ 7,822	$ 7,631
Senior Notes
Debt Instrument [Line Items]
Contractual interest expense	822	629	1,779	1,887
Amortization of debt discount	0	1,422	0	4,217
Amortization of debt issuance costs	1,291	189	3,366	562
Total interest expense	2,113	2,240	5,145	6,666
1.75% Convertible Senior Notes due 2023 | Senior Notes
Debt Instrument [Line Items]
Contractual interest expense	103	629	311	1,887
Amortization of debt discount	0	1,422	0	4,217
Amortization of debt issuance costs	41	189	151	562
Total interest expense	144	2,240	462	6,666
0% Convertible Senior Notes due 2025 | Senior Notes
Debt Instrument [Line Items]
Contractual interest expense	0	0	0	0
Amortization of debt discount	0	0	0	0
Amortization of debt issuance costs	690	0	2,070	0
Total interest expense	690	0	2,070	0
0.5% Convertible Senior Notes Due 2027 | Senior Notes
Debt Instrument [Line Items]
Contractual interest expense	719	0	1,468	0
Amortization of debt discount	0	0	0	0
Amortization of debt issuance costs	560	0	1,145	0
Total interest expense	$ 1,279	$ 0	$ 2,613	$ 0