Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative-effect adjustment from adoption of ASU 2016-09	$ 330,493	$ 338	$ (54,216)	$ 255,936	$ 151,961	$ (23,526)
Beginning balance at Sep. 30, 2018	330,493	$ 338	$ (54,216)	255,936	151,961	(23,526)
Beginning balance (in shares) at Sep. 30, 2018		33,813	6,385
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	9,958				9,958
Other comprehensive income (loss)	(1,989)					(1,989)
Employee stock purchase issuances (in shares)			(111)
Employee stock purchase issuances	1,058		$ 948	110
Repurchase of common stock (in shares)			93
Repurchase of common stock	(1,071)		$ (1,071)
Issuance of stock under stock award plans (in shares)		795
Issuance of stock under stock award plans	4,874	$ 8		4,866
Stock-based compensation expense	5,655			5,655
Ending balance (in shares) at Sep. 30, 2019		34,608	6,367
Ending balance at Sep. 30, 2019	348,978	$ 346	$ (54,339)	266,567	161,919	(25,515)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative-effect adjustment from adoption of ASU 2016-09	348,978	$ 346	$ (54,339)	266,567	161,919	(25,515)
Net income	8,411				8,411
Other comprehensive income (loss)	1,698					1,698
Employee stock purchase issuances (in shares)			(118)
Employee stock purchase issuances	1,065		$ 1,021	44
Repurchase of common stock (in shares)			104
Repurchase of common stock	(1,791)		$ (1,791)
Issuance of stock under stock award plans (in shares)		905
Issuance of stock under stock award plans	5,902	$ 9		5,893
Stock-based compensation expense	7,237			7,237
Ending balance (in shares) at Sep. 30, 2020		35,513	6,353
Ending balance at Sep. 30, 2020	371,500	$ 355	$ (55,109)	279,741	170,330	(23,817)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative-effect adjustment from adoption of ASU 2016-09	371,500	$ 355	$ (55,109)	279,741	170,330	(23,817)
Net income	10,366				10,366
Other comprehensive income (loss)	$ 1,071					1,071
Stock Issued During Period, Shares, New Issues	4,025	4,025
Stock Issued During Period, Value, New Issues	$ 73,830	$ 40		73,790
Stockholders' Equity, Other	(4)				(4)
Employee stock purchase issuances (in shares)			(79)
Employee stock purchase issuances	1,214		$ 694	520
Repurchase of common stock (in shares)			117
Repurchase of common stock	(2,120)		$ (2,120)
Issuance of stock under stock award plans (in shares)		1,115
Issuance of stock under stock award plans	8,525	$ 12		8,513
Stock-based compensation expense	8,135			8,135
Ending balance (in shares) at Sep. 30, 2021		40,653	6,391
Ending balance at Sep. 30, 2021	472,517	$ 407	$ (56,535)	370,699	180,692	(22,746)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative-effect adjustment from adoption of ASU 2016-09	$ 472,517	$ 407	$ (56,535)	$ 370,699	$ 180,692	$ (22,746)