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
Beginning balance at Sep. 30, 2015	$ 274,938	$ 315	$ (54,535)	$ 227,367	$ 124,404	$ (22,613)
Beginning balance (in shares) at Sep. 30, 2015		31,534	6,487
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	16,708				16,708
Other comprehensive income (loss)	(2,078)					(2,078)
Employee stock purchase issuances (in shares)			(104)
Employee stock purchase issuances	896		$ 876	20
Repurchase of common stock (in shares)			48
Repurchase of common stock	(550)		$ (550)
Issuance of stock under stock award plans (in shares)		937
Issuance of stock under stock award plans	7,191	$ 10		7,181
Tax impact from equity awards	(914)			(914)
Accelerated vesting of Etherios stock award plans	184			184
Stock-based compensation expense	3,654			3,654
Ending balance (in shares) at Sep. 30, 2016		32,471	6,431
Ending balance at Sep. 30, 2016	300,029	$ 325	$ (54,209)	237,492	141,112	(24,691)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	9,366				9,366
Other comprehensive income (loss)	2,032					2,032
Employee stock purchase issuances (in shares)			(72)
Employee stock purchase issuances	685		$ 614	71
Repurchase of common stock (in shares)			78
Repurchase of common stock	(938)		$ (938)
Issuance of stock under stock award plans (in shares)		537
Issuance of stock under stock award plans	3,502	$ 5		3,497
Tax impact from equity awards	(191)			(191)
Stock-based compensation expense	4,659			4,659
Ending balance (in shares) at Sep. 30, 2017		33,008	6,437
Ending balance at Sep. 30, 2017	319,144	$ 330	$ (54,533)	245,528	150,478	(22,659)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative-effect adjustment from adoption of ASU 2016-09 | ASU 2016-09	19			52	(33)
Net income	1,303				1,303
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	$ 330,280	$ 338	$ (54,216)	$ 255,936	$ 151,748	$ (23,526)