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	36,525			36,525
Net comprehensive income	36,525			36,525
Stock-based compensation expense (in shares)		411
Stock-based compensation expense	6,060		6,060
Exercises of stock options (in shares)		168
Stock option exercises	631		631
Forfeiture and other settlements of restricted stock (in shares)		(16)
Forfeiture and other settlements of restricted stock	0		0
Common stock redeemed for tax liability (in shares)		(286)
Common stock redeemed for tax liability	(2,620)		(2,620)
Ending balance (in shares) at Mar. 31, 2021		31,289
Ending balance at Mar. 31, 2021	633,767	$ 31	860,537	(226,801)
Beginning balance (in shares) at Dec. 31, 2020		31,254
Beginning balance at Dec. 31, 2020	606,062	$ 31	857,360	(251,329)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	24,528			24,528
Net comprehensive income	24,528			24,528
Stock-based compensation expense	2,549		2,549
Exercises of stock options (in shares)		51
Stock option exercises	628		628
Forfeiture and other settlements of restricted stock (in shares)		(16)
Ending balance (in shares) at Mar. 31, 2021		31,289
Ending balance at Mar. 31, 2021	633,767	$ 31	860,537	(226,801)
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	79,557			79,557
Net comprehensive income	79,557			79,557
Stock-based compensation expense (in shares)		517
Stock-based compensation expense	4,532		4,532
Exercises of stock options (in shares)		1
Stock option exercises	4		4
Forfeiture and other settlements of restricted stock (in shares)		(47)
Forfeiture and other settlements of restricted stock	0
Common stock redeemed for tax liability (in shares)		(307)
Common stock redeemed for tax liability	(6,620)		(6,620)
Ending balance (in shares) at Mar. 31, 2022		31,458
Ending balance at Mar. 31, 2022	802,357	$ 31	864,074	(61,748)
Beginning balance (in shares) at Dec. 31, 2021		31,460
Beginning balance at Dec. 31, 2021	755,259	$ 31	861,648	(106,420)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	44,672			44,672
Net comprehensive income	$ 44,672			44,672
Stock-based compensation expense (in shares)	1
Stock-based compensation expense	$ 2,424		2,424
Stock option exercises	4		4
Forfeiture and other settlements of restricted stock (in shares)		(3)
Forfeiture and other settlements of restricted stock	0
Common stock redeemed for tax liability	(2)		(2)
Ending balance (in shares) at Mar. 31, 2022		31,458
Ending balance at Mar. 31, 2022	$ 802,357	$ 31	$ 864,074	$ (61,748)