Long-term Debt - Interest Expense on Note (Details) - Senior Notes [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Coupon interest	$ 2,200	$ 3,414	$ 1,043
Amortization of debt discount	2,561	3,773	1,111
Amortization of debt issuance costs	533	824	252
Total interest expense recognized	5,294	8,011	2,406
Convertible Senior Notes Due 2025
Debt Instrument [Line Items]
Coupon interest	1,094	0	0
Amortization of debt discount	3,254	0	0
Amortization of debt issuance costs	438	0	0
Total interest expense recognized	$ 4,786	$ 0	$ 0