Condensed Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock	Treasury Stock	Accumulated Other Comprehensive Income	Accumulated Deficit	Total
Beginning balance (in shares) at Sep. 30, 2018	27,577
Common Stock, Number of Shares [Abstract]
Stock-based compensation (in shares)	212
Stock option exercises (in shares)	1
Issuance of common stock - ESPP (in shares)	66
Issuance of common stock - ESPP	$ 237
Ending balance (in shares) at Mar. 31, 2019	27,856
Balance, beginning of period at Sep. 30, 2018	$ 734,066		$ 885	$ (580,425)
Common Stock, Number of Shares [Abstract]
Stock-based compensation	1,147
Stock option exercises	1
Tax withholding paid on behalf of employees for stock-based awards	(194)
Issuance of common stock - ESPP	237
Translation adjustment			27		$ 27
Net loss				(10,532)	(10,532)
Balance, end of period at Mar. 31, 2019	$ 735,257	$ (47,721)	912	(590,957)	97,491
Beginning balance (in shares) at Dec. 31, 2018	27,668
Common Stock, Number of Shares [Abstract]
Stock-based compensation (in shares)	121
Stock option exercises (in shares)	1
Issuance of common stock - ESPP (in shares)	66
Issuance of common stock - ESPP	$ 237
Ending balance (in shares) at Mar. 31, 2019	27,856
Balance, beginning of period at Dec. 31, 2018	$ 734,341		899	(585,963)
Common Stock, Number of Shares [Abstract]
Stock-based compensation	722
Stock option exercises	1
Tax withholding paid on behalf of employees for stock-based awards	(44)
Issuance of common stock - ESPP	237
Translation adjustment			13		13
Net loss				(4,994)	(4,994)
Balance, end of period at Mar. 31, 2019	$ 735,257	(47,721)	912	(590,957)	$ 97,491
Beginning balance (in shares) at Sep. 30, 2019	28,893				28,893
Common Stock, Number of Shares [Abstract]
Stock-based compensation (in shares)	166
Stock option exercises (in shares)	1
Issuance of restricted stock units (shares)					116
Issuance of restricted stock units					$ 410
Issuance of common stock - ESPP (in shares)	115
Issuance of common stock - ESPP	$ 279
Ending balance (in shares) at Mar. 31, 2020	29,291				29,291
Balance, beginning of period at Sep. 30, 2019	$ 739,926		950	(616,409)
Common Stock, Number of Shares [Abstract]
Stock-based compensation	1,846
Stock option exercises	2
Tax withholding paid on behalf of employees for stock-based awards	(47)
Issuance of common stock - ESPP	279
Translation adjustment			(7)		$ (7)
Net loss				(6,416)	(6,416)
Balance, end of period at Mar. 31, 2020	$ 742,416	(47,721)	943	(622,825)	$ 72,813
Beginning balance (in shares) at Dec. 31, 2019	28,948
Common Stock, Number of Shares [Abstract]
Stock-based compensation (in shares)	111
Stock option exercises (in shares)	1
Issuance of restricted stock units (shares)					116
Issuance of restricted stock units					$ 410
Issuance of common stock - ESPP (in shares)	115
Issuance of common stock - ESPP	$ 279
Ending balance (in shares) at Mar. 31, 2020	29,291				29,291
Balance, beginning of period at Dec. 31, 2019	$ 740,680		914	(617,744)
Common Stock, Number of Shares [Abstract]
Stock-based compensation	1,045
Stock option exercises	2
Issuance of common stock - ESPP	279
Translation adjustment			29		$ 29
Net loss				(5,081)	(5,081)
Balance, end of period at Mar. 31, 2020	$ 742,416	$ (47,721)	$ 943	$ (622,825)	$ 72,813