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, 2018	1,648	55,689
Beginning balance, value at Apr. 30, 2018	$ 2	$ 55	$ 614,810	$ (559,129)	$ 55,738
Series E preferred stock dividends			(3,244)		(3,244)
Cumulative-effect adjustment to accumulated deficit pursuant to adoption of ASU				2,739	2,739
Common stock issued under Employee Stock Purchase Plan, shares		40
Common stock issued under Employee Stock Purchase Plan, value			114		114
Exercise of stock options, shares		343
Exercise of stock options, value		$ 1	1,187		1,188
Stock-based compensation expense			1,080		1,080
Net loss				(4,551)	(4,551)
Ending balance, shares at Jan. 31, 2019	1,648	56,072
Ending balance, value at Jan. 31, 2019	$ 2	$ 56	613,947	(560,941)	53,064
Beginning balance, shares at Oct. 31, 2018	1,648	56,063
Beginning balance, value at Oct. 31, 2018	$ 2	$ 56	614,541	(559,802)	54,797
Series E preferred stock dividends			(1,081)		(1,081)
Exercise of stock options, shares		9
Exercise of stock options, value			29		29
Stock-based compensation expense			458		458
Net loss				(1,139)	(1,139)
Ending balance, shares at Jan. 31, 2019	1,648	56,072
Ending balance, value at Jan. 31, 2019	$ 2	$ 56	613,947	(560,941)	53,064
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
Vesting of restricted stock units		49
Stock-based compensation expense			1,849		1,849
Net 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
Vesting of restricted stock units		21
Stock-based compensation expense			595		595
Net 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