Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning balance (in shares) at Sep. 30, 2018		33,813	6,385
Beginning balance at Sep. 30, 2018	$ 330,493	$ 338	$ (54,216)	$ 255,936	$ 151,961	$ (23,526)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	7,672				7,672
Other comprehensive income (loss)	(1,107)					(1,107)
Employee stock purchase plan issuances (in shares)			(91)
Employee stock purchase plan issuances	835		$ 773	62
Repurchase of common stock (in shares)			92
Repurchase of common stock	(1,051)		$ (1,051)
Issuance of stock under stock award plans (in shares)		698
Issuance of stock under stock award plans	4,054	$ 7		4,047
Stock-based compensation expense	4,180			4,180
Ending balance (in shares) at Jun. 30, 2019		34,511	6,386
Ending balance at Jun. 30, 2019	345,076	$ 345	$ (54,494)	264,225	159,633	(24,633)
Beginning balance (in shares) at Sep. 30, 2019		34,608	6,367
Beginning balance at Sep. 30, 2019	348,978	$ 346	$ (54,339)	266,567	161,919	(25,515)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	3,978				3,978
Other comprehensive income (loss)	857					857
Employee stock purchase plan issuances (in shares)			(90)
Employee stock purchase plan issuances	798		$ 783	15
Repurchase of common stock (in shares)			96
Repurchase of common stock	(1,692)		$ (1,692)
Issuance of stock under stock award plans (in shares)		797
Issuance of stock under stock award plans	5,063	$ 8		5,055
Stock-based compensation expense	5,323			5,323
Ending balance (in shares) at Jun. 30, 2020		35,405	6,373
Ending balance at Jun. 30, 2020	$ 363,305	$ 354	$ (55,248)	$ 276,960	$ 165,897	$ (24,658)