Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Paid-in Capital	Accumulated Deficit
Beginning balance (in shares) at Sep. 30, 2019		30,933,000
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	13,360			13,360
Stock-based compensation expense	3,210		3,210
Exercises of stock options (in shares)		50,000
Exercises of stock options	204		204
Shares issued under employee stock plans, net (in shares)		581,000
Forfeiture and other settlements of restricted stock (in shares)		(11,000)
Forfeiture and other settlements of restricted stock	(2,058)		(2,058)
Common stock redeemed for tax liability (in shares)		(171,000)
Common stock redeemed for tax liability	(2,661)		(2,661)
Share repurchases (in shares)		(362,000)
Share repurchases	(3,327)	$ 0	(3,327)
Ending balance (in shares) at Mar. 31, 2020		31,020,000
Ending balance at Mar. 31, 2020	547,482	$ 31	849,643	(302,192)
Beginning balance (in shares) at Sep. 30, 2019		30,933,000
Beginning balance at Sep. 30, 2019	538,754	$ 31	854,275	(315,552)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share repurchases	(3,300)
Ending balance (in shares) at Sep. 30, 2020		31,012,000
Ending balance at Sep. 30, 2020	593,171	$ 31	856,466	(263,326)
Beginning balance (in shares) at Dec. 31, 2019		31,383,000
Beginning balance at Dec. 31, 2019	539,280	$ 31	852,055	(312,806)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income and comprehensive income	10,614			10,614
Stock-based compensation expense	899		899
Exercises of stock options (in shares)		3,000
Exercises of stock options	31		31
Shares issued under employee stock plans, net (in shares)		7,000
Forfeiture and other settlements of restricted stock (in shares)		(10,000)
Common stock redeemed for tax liability (in shares)		(1,000)
Common stock redeemed for tax liability	(15)		(15)
Share repurchases (in shares)		(362,000)
Share repurchases	(3,327)	$ 0	(3,327)
Ending balance (in shares) at Mar. 31, 2020		31,020,000
Ending balance at Mar. 31, 2020	547,482	$ 31	849,643	(302,192)
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	36,525			36,525
Stock-based compensation expense	6,060		6,060
Exercises of stock options (in shares)		168,000
Exercises of stock options	631		631
Shares issued under employee stock plans, net (in shares)		411,000
Forfeiture and other settlements of restricted stock (in shares)		(16,000)
Forfeiture and other settlements of restricted stock	0		0
Common stock redeemed for tax liability (in shares)		(286,000)
Common stock redeemed for tax liability	$ (2,620)		(2,620)
Share repurchases (in shares)	0
Ending balance (in shares) at Mar. 31, 2021		31,289,000
Ending balance at Mar. 31, 2021	$ 633,767	$ 31	860,537	(226,801)
Beginning balance (in shares) at Dec. 31, 2020		31,254,000
Beginning balance at Dec. 31, 2020	606,062	$ 31	857,360	(251,329)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income and comprehensive income	24,528			24,528
Stock-based compensation expense	2,549		2,549
Exercises of stock options (in shares)		51,000
Exercises of stock options	628		628
Forfeiture and other settlements of restricted stock (in shares)		(16,000)
Forfeiture and other settlements of restricted stock	$ 0		0
Share repurchases (in shares)	0
Ending balance (in shares) at Mar. 31, 2021		31,289,000
Ending balance at Mar. 31, 2021	$ 633,767	$ 31	$ 860,537	$ (226,801)