Convertible Senior Notes - Conversion (Details) - USD ($) $ in Thousands		1 Months Ended	6 Months Ended
	May 18, 2020	May 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Jan. 07, 2021	Dec. 31, 2020	May 29, 2020	Mar. 31, 2018
Convertible Senior Notes
Net proceeds			$ 32,159	$ 27,678
5.5% Convertible Senior Notes
Convertible Senior Notes
Principal amount	$ 100,000				$ 160	$ 33,500		$ 100,000
3.75% Convertible Senior Notes
Convertible Senior Notes
Principal amount	200,000	$ 212,463	$ 197,278				$ 12,500
Less initial purchasers' discount	(6,400)	(6,374)
Less cost of related capped calls		(16,253)
Less other issuance costs	$ (600)	(617)
Net proceeds		$ 189,219