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	11,997			11,997
Net comprehensive income	11,997			11,997
Stock-based compensation expense	3,511		3,511
Exercises of stock options (in shares)		117
Stock option exercises	3		3
Shares issued under employee stock plans, net (in shares)		411
Common stock redeemed for tax liability (in shares)		(286)
Common stock redeemed for tax liability	(2,620)		(2,620)
Ending balance (in shares) at Dec. 31, 2020		31,254
Ending balance at Dec. 31, 2020	606,062	$ 31	857,360	(251,329)
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	34,885			34,885
Net comprehensive income	34,885			34,885
Stock-based compensation expense	2,108		2,108
Shares issued under employee stock plans, net (in shares)		517
Forfeiture and other settlements of restricted stock (in shares)		(44)
Common stock redeemed for tax liability (in shares)		(307)
Common stock redeemed for tax liability	(6,618)		(6,618)
Ending balance (in shares) at Dec. 31, 2021		31,460
Ending balance at Dec. 31, 2021	$ 755,259	$ 31	$ 861,648	$ (106,420)