Convertible Senior Notes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020	Jun. 30, 2020	May 31, 2020	May 29, 2020	May 18, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Mar. 31, 2018
Convertible Senior Notes
Net carrying amount	$ 85,640	$ 110,431	$ 105,088	$ 142,889				$ 113,063	$ 107,945	$ 66,844	$ 65,025
3.75% Convertible Senior Notes
Convertible Senior Notes
Principal amount	212,463				$ 212,463	$ 12,500	$ 200,000
Unamortized debt discount	(124,655)
Unamortized debt issuance costs	(2,295)
Net carrying amount	85,513
Carrying amount of the equity component	130,249						130,300
Income tax benefit on equity component	29,800
5.5% Convertible Senior Notes
Convertible Senior Notes
Principal amount	160	100,000					$ 100,000					$ 100,000
Unamortized debt discount	(32)	(27,818)
Unamortized debt issuance costs	(1)	(1,567)
Net carrying amount	$ 127	70,615
Carrying amount of the equity component		37,702			$ 37,700
Income tax benefit on equity component		$ 9,200