CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Paid-in Capital	Accumulated Deficit
Beginning balance (in shares) at Sep. 30, 2020		31,012
Beginning balance at Sep. 30, 2020	$ 593,171	$ 31	$ 856,466	$ (263,326)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	73,660			73,660
Net comprehensive income	73,660			73,660
Stock-based compensation expense	9,254		9,254
Exercises of stock options (in shares)		198
Stock option exercises	564		564
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)
Ending balance (in shares) at Jun. 30, 2021		31,294
Ending balance at Jun. 30, 2021	673,605	$ 31	863,240	(189,666)
Beginning balance (in shares) at Mar. 31, 2021		31,289
Beginning balance at Mar. 31, 2021	633,767	$ 31	860,537	(226,801)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	37,135			37,135
Net comprehensive income	37,135			37,135
Stock-based compensation expense	3,194		3,194
Exercises of stock options (in shares)		30
Stock option exercises	(67)		(67)
Shares issued under employee stock plans, net (in shares)		6
Forfeiture and other settlements of restricted stock (in shares)		(13)
Common stock redeemed for tax liability (in shares)		(18)
Common stock redeemed for tax liability	(424)		(424)
Ending balance (in shares) at Jun. 30, 2021		31,294
Ending balance at Jun. 30, 2021	673,605	$ 31	863,240	(189,666)
Beginning balance (in shares) at Sep. 30, 2021		31,294
Beginning balance at Sep. 30, 2021	724,884	$ 31	866,158	(141,305)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	133,881			133,881
Net comprehensive income	133,881			133,881
Stock-based compensation expense	6,515		6,515
Exercises of stock options (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
Common stock redeemed for tax liability (in shares)		(308)
Common stock redeemed for tax liability	(6,631)		(6,631)
Share repurchases (in shares)		(175)
Share repurchases	(2,527)		(2,527)
Ending balance (in shares) at Jun. 30, 2022		31,275
Ending balance at Jun. 30, 2022	856,127	$ 31	863,520	(7,424)
Beginning balance (in shares) at Mar. 31, 2022		31,458
Beginning balance at Mar. 31, 2022	802,357	$ 31	864,074	(61,748)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	54,324			54,324
Net comprehensive income	54,324			54,324
Stock-based compensation expense	1,983		1,983
Exercises of stock options (in shares)		0
Stock option exercises	1		1
Shares issued under employee stock plans, net (in shares)		1
Forfeiture and other settlements of restricted stock (in shares)		(8)
Forfeiture and other settlements of restricted stock	0
Common stock redeemed for tax liability (in shares)		(1)
Common stock redeemed for tax liability	(11)		(11)
Share repurchases (in shares)		(175)
Share repurchases	(2,527)		(2,527)
Ending balance (in shares) at Jun. 30, 2022		31,275
Ending balance at Jun. 30, 2022	$ 856,127	$ 31	$ 863,520	$ (7,424)