CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Paid-in Capital	(Accumulated Deficit) Retained Earnings
Beginning balance (in shares) at Sep. 30, 2019		30,933
Beginning balance at Sep. 30, 2019	$ 538,754	$ 31	$ 854,275	$ (315,552)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income and comprehensive income	52,226			52,226
Stock-based compensation expense	10,036		10,036
Stock option exercises (in shares)		52
Stock option exercises	226		226
Shares issued under employee stock plans, net (in shares)		588
Forfeiture and other settlements of restricted stock (in shares)		(26)
Forfeiture and other settlements of restricted stock	(2,058)		(2,058)
Common stock redeemed for tax liability (in shares)		(173)
Common stock redeemed for tax liability	$ (2,686)		(2,686)
Share repurchases (in shares)	(362)	(362)
Share repurchases	$ (3,327)		(3,327)
Ending balance (in shares) at Sep. 30, 2020		31,012
Ending balance at Sep. 30, 2020	593,171	$ 31	856,466	(263,326)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income and comprehensive income	122,021			122,021
Stock-based compensation expense	12,167		12,167
Stock option exercises (in shares)		198
Stock option exercises	569		569
Shares issued under employee stock plans, net (in shares)		417
Forfeiture and other settlements of restricted stock (in shares)		(29)
Forfeiture and other settlements of restricted stock	0		0
Common stock redeemed for tax liability (in shares)		(304)
Common stock redeemed for tax liability	(3,044)		(3,044)
Share repurchases	0
Ending balance (in shares) at Sep. 30, 2021		31,294
Ending balance at Sep. 30, 2021	724,884	$ 31	866,158	(141,305)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income and comprehensive income	220,704			220,704
Stock-based compensation expense	8,478		8,478
Stock option exercises (in shares)		1
Stock option exercises	5		5
Shares issued under employee stock plans, net (in shares)		518
Forfeiture and other settlements of restricted stock (in shares)		(55)
Forfeiture and other settlements of restricted stock	0		0
Common stock redeemed for tax liability (in shares)		(308)
Common stock redeemed for tax liability	$ (6,631)		(6,631)
Share repurchases (in shares)	(570)	(570)
Share repurchases	$ (8,154)		(8,154)
Ending balance (in shares) at Sep. 30, 2022		30,880
Ending balance at Sep. 30, 2022	$ 939,286	$ 31	$ 859,856	$ 79,399