Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment [Member]	Common Stock	Treasury Stock	Additional Paid-in Capital	Additional Paid-in Capital Cumulative Effect, Period of Adoption, Adjustment [Member]	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment [Member]	Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative-effect adjustment from adoption of ASU 2016-09	$ 319,029	$ 19	$ 330	$ (54,533)	$ 245,528	$ 52	$ 150,363	$ (33)	$ (22,659)
Beginning balance at Sep. 30, 2017	319,029	19	$ 330	$ (54,533)	245,528	52	150,363	(33)	(22,659)
Beginning balance (in shares) at Sep. 30, 2017			33,008	6,437
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative-effect adjustment from adoption of ASU 2016-09	330,493	$ 19	$ 338	$ (54,216)	255,936	$ 52	151,961	$ (33)	(23,526)
Net income	1,631						1,631
Other comprehensive income (loss)	(867)								(867)
Employee stock purchase issuances (in shares)				(126)
Employee stock purchase issuances	1,115			$ 1,065	50
Repurchase of common stock (in shares)				74
Repurchase of common stock	(748)			$ (748)
Issuance of stock under stock award plans (in shares)			805
Issuance of stock under stock award plans	5,460		$ 8		5,452
Stock-based compensation expense	4,854				4,854
Ending balance (in shares) at Sep. 30, 2018			33,813	6,385
Ending balance at Sep. 30, 2018	330,493		$ 338	$ (54,216)	255,936		151,961		(23,526)
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)
Cumulative-effect adjustment from adoption of ASU 2016-09	348,978		$ 346	$ (54,339)	266,567		161,919		(25,515)
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)
Cumulative-effect adjustment from adoption of ASU 2016-09	348,978		$ 355	$ (55,109)	279,741		170,330		(23,817)
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)