CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Paid-in Capital	(Accumulated Deficit) Retained Earnings
Beginning balance (in shares) at Sep. 30, 2020		31,012,000
Beginning 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)		198,000
Stock option exercises	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)
Share repurchases (in shares)	0
Ending balance (in shares) at Sep. 30, 2021		31,294,000
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)		1,000
Stock option exercises	5		5
Shares issued under employee stock plans, net (in shares)		518,000
Forfeiture and other settlements of restricted stock (in shares)		(55,000)
Forfeiture and other settlements of restricted stock	0		0
Common stock redeemed for tax liability (in shares)		(308,000)
Common stock redeemed for tax liability	$ (6,631)		(6,631)
Share repurchases (in shares)	(570,000)	(570,000)
Share repurchases	$ (8,154)		(8,154)
Other activity	0		0
Ending balance (in shares) at Sep. 30, 2022		30,880,000
Ending balance at Sep. 30, 2022	939,286	$ 31	859,856	79,399
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income and comprehensive income	158,611			158,611
Stock-based compensation expense	7,275		7,275
Stock option exercises (in shares)		14,000
Stock option exercises	262		262
Shares issued under employee stock plans, net (in shares)		675,000
Forfeiture and other settlements of restricted stock (in shares)		(12,000)
Forfeiture and other settlements of restricted stock	0		0
Common stock redeemed for tax liability (in shares)		(206,000)
Common stock redeemed for tax liability	$ (2,615)		(2,615)
Share repurchases (in shares)	0
Ending balance (in shares) at Sep. 30, 2023		31,351,000
Ending balance at Sep. 30, 2023	$ 1,102,819	$ 31	$ 864,778	$ 238,010