Convertible Senior Notes - Conversion (Details) - USD ($) $ in Thousands		1 Months Ended		6 Months Ended
	Jun. 10, 2020	May 31, 2020	Mar. 31, 2018	Jun. 30, 2020	Jun. 30, 2019	May 18, 2020	Dec. 31, 2019
Convertible Senior Notes
Net proceeds	$ 25,000			$ 27,678	$ 25,609
5.5% Convertible Senior Notes
Convertible Senior Notes
Principal amount		$ 1,000	$ 100,000	33,660		$ 100,000	$ 100,000
Less initial purchasers' discount		(3,300)	(3,250)
Less cost of related capped call and common stock forward			(43,500)
Less other issuance costs		$ (900)	(894)	$ (1,700)
Net proceeds			$ 52,356