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			(1,081)		(1,081)
Cumulative-effect adjustment to accumulated deficit pursuant to adoption of ASU				2,739	2,739
Exercise of stock options, shares		301
Exercise of stock options, value			1,014		1,014
Stock-based compensation expense			297		297
Net loss				(1,961)	(1,961)
Ending balance, shares at Jul. 31, 2018	1,648	55,990
Ending balance, value at Jul. 31, 2018	$ 2	$ 55	615,040	(558,351)	56,746
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			(1,081)		(1,081)
Exercise of stock options, shares		74
Exercise of stock options, value			258		258
Vesting of restricted stock units		28
Stock-based compensation expense			603		603
Net loss				(3,164)	(3,164)
Ending balance, shares at Jul. 31, 2019	1,648	56,238
Ending balance, value at Jul. 31, 2019	$ 2	$ 56	$ 613,395	$ (563,769)	$ 49,684