Convertible Senior Notes - Conversion (Details) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended
	Mar. 08, 2018	Mar. 31, 2018	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019
Convertible Senior Notes
Principal amount		$ 100,000
Net proceeds			$ 9,024
$100M Convertible Senior Notes
Convertible Senior Notes
Principal amount	$ 100,000	100,000	100,000	$ 100,000	$ 1,000
Less initial purchasers' discount	(3,250)
Less initial purchasers' discount	(3,300)
Less cost of related capped call and common stock forward	(43,500)	(43,500)
Less other issuance costs	(894)		$ (1,700)
Net proceeds	$ 52,356	$ 95,900