Debt - Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jul. 23, 2018
Debt Instrument [Line Items]
Total amortization of debt issuance costs and accretion of equity portion			$ 5,254	$ 4,674
Total interest expense related to the Notes	$ 2,522	$ 2,274	7,631	6,564
1.75% Convertible Senior Notes due 2023
Debt Instrument [Line Items]
Amortization of debt discount	1,422	1,359	4,217	4,031
Amortization of debt issuance costs	189	182	562	541
Total amortization of debt issuance costs and accretion of equity portion	1,611	1,541	4,779	4,572
Contractual interest expense	629	629	1,887	1,887
Total interest expense related to the Notes	$ 2,240	$ 2,170	$ 6,666	$ 6,459
Effective interest rate of the liability component					7.25%