CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Total
Beginning balance, value at Apr. 30, 2020	$ 2	$ 56	$ 612,909	$ (571,071)	$ 41,896
Beginning balance, shares at Apr. 30, 2020	1,648	56,483
Series E preferred stock dividends paid ($0.65625 per share)			(1,081)		(1,081)
Common stock issued under equity compensation plans			264		264
Common stock issued under equity compensation plans, Shares		118
Stock-based compensation expense			730		730
Net income				4,730	4,730
Ending balance, value at Jul. 31, 2020	$ 2	$ 56	612,822	(566,341)	46,539
Ending balance, shares at Jul. 31, 2020	1,648	56,601
Beginning balance, value at Apr. 30, 2021		$ 61	637,534	(559,859)	77,736
Beginning balance, shares at Apr. 30, 2021		61,069
Cumulative-effect adjustment from modified retrospective adoption of ASU 2020-06			(42,431)	810	(41,621)
Common stock issued under equity compensation plans			918		918
Common stock issued under equity compensation plans, Shares		272
Stock-based compensation expense			1,299		1,299
Net income				6,304	6,304
Ending balance, value at Jul. 31, 2021		$ 61	$ 597,320	$ (552,745)	$ 44,636
Ending balance, shares at Jul. 31, 2021		61,341