CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Paid-in Capital	Accumulated Deficit
Beginning balance (in shares) at Sep. 30, 2018		33,522,000
Beginning balance at Sep. 30, 2018	$ 644,027	$ 34	$ 880,025	$ (236,032)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income and comprehensive (loss) income	(79,520)			(79,520)
Stock-based compensation expense	$ 10,526		10,526
Exercises of stock options (in shares)	31,450	32,000
Exercises of stock options	$ 314		314
Shares issued under employee stock plans, net (in shares)		917,000
Forfeiture and other settlements of restricted stock (in shares)		(68,000)
Common stock redeemed for tax liability (in shares)		(185,000)
Common stock redeemed for tax liability	(1,969)		(1,969)
Share repurchases (in shares)		(3,285,000)
Share repurchases	(34,624)	$ (3)	(34,621)
Ending balance (in shares) at Sep. 30, 2019		30,933,000
Ending balance at Sep. 30, 2019	538,754	$ 31	854,275	(315,552)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income and comprehensive (loss) income	52,226			52,226
Stock-based compensation expense	$ 10,036		10,036
Exercises of stock options (in shares)	128,921	52,000
Exercises of stock options	$ 226		226
Shares issued under employee stock plans, net (in shares)		588,000
Forfeiture and other settlements of restricted stock (in shares)		(26,000)
Forfeiture and other settlements of restricted stock	(2,058)		(2,058)
Common stock redeemed for tax liability (in shares)		(173,000)
Common stock redeemed for tax liability	(2,686)		(2,686)
Share repurchases (in shares)		(362,000)
Share repurchases	(3,327)	$ 0	(3,327)
Ending balance (in shares) at Sep. 30, 2020		31,012,000
Ending balance at Sep. 30, 2020	593,171	$ 31	856,466	(263,326)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income and comprehensive (loss) income	122,021			122,021
Stock-based compensation expense	$ 12,167		12,167
Exercises of stock options (in shares)	278,206	198,000
Exercises of stock options	$ 569		569
Shares issued under employee stock plans, net (in shares)		417,000
Forfeiture and other settlements of restricted stock (in shares)		(29,000)
Forfeiture and other settlements of restricted stock	0		0
Common stock redeemed for tax liability (in shares)		(304,000)
Common stock redeemed for tax liability	(3,044)		(3,044)
Ending balance (in shares) at Sep. 30, 2021		31,294,000
Ending balance at Sep. 30, 2021	$ 724,884	$ 31	$ 866,158	$ (141,305)