CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Total
Beginning balance, shares at Apr. 30, 2019	1,648	56,136
Beginning balance, value at Apr. 30, 2019	$ 2	$ 56	$ 613,615	$ (560,605)	$ 53,068
Series E preferred stock dividends			(3,244)		(3,244)
Common stock issued under Employee Stock Purchase Plan, shares		47
Common stock issued under Employee Stock Purchase Plan, value			187		187
Exercise of stock options, shares		247
Exercise of stock options, value			916		916
Common stock issued upon vesting of restricted stock units, shares		49
Common stock issued upon vesting of restricted stock units, value
Stock-based compensation expense			1,849		1,849
Net income (loss)				(5,698)	(5,698)
Ending balance, shares at Jan. 31, 2020	1,648	56,479
Ending balance, value at Jan. 31, 2020	$ 2	$ 56	613,323	(566,303)	47,078
Beginning balance, shares at Oct. 31, 2019	1,648	56,338
Beginning balance, value at Oct. 31, 2019	$ 2	$ 56	613,325	(564,199)	49,184
Series E preferred stock dividends			(1,081)		(1,081)
Exercise of stock options, shares		120
Exercise of stock options, value			484		484
Common stock issued upon vesting of restricted stock units, shares		21
Common stock issued upon vesting of restricted stock units, value
Stock-based compensation expense			595		595
Net income (loss)				(2,104)	(2,104)
Ending balance, shares at Jan. 31, 2020	1,648	56,479
Ending balance, value at Jan. 31, 2020	$ 2	$ 56	613,323	(566,303)	47,078
Beginning balance, shares at Apr. 30, 2020	1,648	56,483
Beginning balance, value at Apr. 30, 2020	$ 2	$ 56	612,909	(571,071)	41,896
Series E preferred stock dividends			(3,244)		(3,244)
Common stock issued, net of issuance, shares		3,833
Common stock issued, net of issuance, value		$ 4	32,137		32,141
Common stock issued under Employee Stock Purchase Plan, shares		72
Common stock issued under Employee Stock Purchase Plan, value			423		423
Exercise of stock options, shares		354
Exercise of stock options, value		$ 1	2,178		2,179
Common stock issued upon vesting of restricted stock units, shares		85
Common stock issued upon vesting of restricted stock units, value
Stock-based compensation expense			2,754		2,754
Net income (loss)				9,221	9,221
Ending balance, shares at Jan. 31, 2021	1,648	60,827
Ending balance, value at Jan. 31, 2021	$ 2	$ 61	647,157	(561,850)	85,370
Beginning balance, shares at Oct. 31, 2020	1,648	56,722
Beginning balance, value at Oct. 31, 2020	$ 2	$ 57	613,384	(564,057)	49,386
Series E preferred stock dividends			(1,081)		(1,081)
Common stock issued, net of issuance, shares		3,833
Common stock issued, net of issuance, value		$ 4	32,137		32,141
Common stock issued under Employee Stock Purchase Plan, shares		40
Common stock issued under Employee Stock Purchase Plan, value			244		244
Exercise of stock options, shares		213
Exercise of stock options, value			1,474		1,474
Common stock issued upon vesting of restricted stock units, shares		19
Common stock issued upon vesting of restricted stock units, value
Stock-based compensation expense			999		999
Net income (loss)				2,207	2,207
Ending balance, shares at Jan. 31, 2021	1,648	60,827
Ending balance, value at Jan. 31, 2021	$ 2	$ 61	$ 647,157	$ (561,850)	$ 85,370