Condensed Consolidated Statements of Shareholders' Equity (unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Treasury Stock	Accumulated Other Comprehensive Income	Accumulated Deficit
Beginning balance (in shares) at Sep. 30, 2019		28,893
Shares of Common Stock
Stock-based compensation (in shares)		283
Stock option exercises (in shares)		1
Issuance of restricted stock units (in shares)		116
Issuance of common stock - ESPP (in shares)		115
Sale of common stock (in shares)		0
Ending balance (in shares) at Jun. 30, 2020		29,408
Balance, beginning of period at Sep. 30, 2019		$ 739,926	$ (47,721)	$ 950	$ (616,409)
Shares of Common Stock
Stock-based compensation		2,625
Stock option exercises		2
Tax withholding paid on behalf of employees for stock-based awards		(82)
Issuance of restricted stock units		410
Issuance of common stock - ESPP		279
Sale of common stock, net of offering costs		0
Translation adjustment	$ (5)			(5)
Net income (loss)	(7,703)				(7,703)
Balance, end of period at Jun. 30, 2020	72,272	$ 743,160	(47,721)	945	(624,112)
Beginning balance (in shares) at Mar. 31, 2020		29,291
Shares of Common Stock
Stock-based compensation (in shares)		117
Stock option exercises (in shares)		0
Issuance of restricted stock units (in shares)		0
Issuance of common stock - ESPP (in shares)		0
Sale of common stock (in shares)		0
Ending balance (in shares) at Jun. 30, 2020		29,408
Balance, beginning of period at Mar. 31, 2020		$ 742,416	(47,721)	943	(622,825)
Shares of Common Stock
Stock-based compensation		779
Stock option exercises		0
Tax withholding paid on behalf of employees for stock-based awards		(35)
Issuance of restricted stock units		0
Issuance of common stock - ESPP		0
Sale of common stock, net of offering costs		0
Translation adjustment	2			2
Net income (loss)	(1,287)				(1,287)
Balance, end of period at Jun. 30, 2020	$ 72,272	$ 743,160	(47,721)	945	(624,112)
Beginning balance (in shares) at Sep. 30, 2020	29,551	29,551
Shares of Common Stock
Stock-based compensation (in shares)		534
Stock option exercises (in shares)		15
Issuance of restricted stock units (in shares)		0
Issuance of common stock - ESPP (in shares)		126
Sale of common stock (in shares)		6,655
Ending balance (in shares) at Jun. 30, 2021	36,881	36,881
Balance, beginning of period at Sep. 30, 2020		$ 744,361	(47,721)	918	(623,409)
Shares of Common Stock
Stock-based compensation		3,010
Stock option exercises		77
Tax withholding paid on behalf of employees for stock-based awards		(195)
Issuance of restricted stock units		0
Issuance of common stock - ESPP		382
Sale of common stock, net of offering costs		33,141
Translation adjustment	$ (26)			(26)
Net income (loss)	20,568				20,568
Balance, end of period at Jun. 30, 2021	$ 131,106	$ 780,776	(47,721)	892	(602,841)
Beginning balance (in shares) at Mar. 31, 2021		36,775
Shares of Common Stock
Stock-based compensation (in shares)		101
Stock option exercises (in shares)		5
Issuance of restricted stock units (in shares)		0
Issuance of common stock - ESPP (in shares)		0
Sale of common stock (in shares)		0
Ending balance (in shares) at Jun. 30, 2021	36,881	36,881
Balance, beginning of period at Mar. 31, 2021		$ 779,681	(47,721)	897	(616,456)
Shares of Common Stock
Stock-based compensation		1,176
Stock option exercises		31
Tax withholding paid on behalf of employees for stock-based awards		(112)
Issuance of restricted stock units		0
Issuance of common stock - ESPP		0
Sale of common stock, net of offering costs		0
Translation adjustment	$ (5)			(5)
Net income (loss)	13,615				13,615
Balance, end of period at Jun. 30, 2021	$ 131,106	$ 780,776	$ (47,721)	$ 892	$ (602,841)