CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - 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			(4,325)		(4,325)
Cumulative-effect adjustment to accumulated deficit pursuant to adoption of ASU				2,739	2,739
Common stock issued under equity compensation plans, shares		446
Common stock issued under equity compensation plans, value		$ 1	1,535		1,536
Stock-based compensation expense			1,595		1,595
Net income				(4,215)	(4,215)
Ending balance, shares at Apr. 30, 2019	1,648	56,135
Ending balance, value at Apr. 30, 2019	$ 2	$ 56	613,615	(560,605)	53,068
Series E preferred stock dividends			(4,325)		(4,325)
Common stock issued under equity compensation plans, shares		348
Common stock issued under equity compensation plans, value			1,120		1,120
Stock-based compensation expense			2,499		2,499
Net income				(10,466)	(10,466)
Ending balance, shares at Apr. 30, 2020	1,648	56,483
Ending balance, value at Apr. 30, 2020	$ 2	$ 56	612,909	(571,071)	41,896
Series E preferred stock dividends			(4,455)		(4,455)
Conversion of Series E preferred stock to common stock, shares converted	(28)
Conversion of Series E preferred stock to common stock, shares issued		34
Redemption of Series E preferred stock, shares	(1,620)
Redemption of Series E preferred stock, value	$ (2)		(40,488)		(40,490)
Common stock issued, net of issuance costs, shares		3,833
Common stock issued, net of issuance costs, value		$ 4	32,137		32,141
Common stock issued under equity compensation plans, shares		719
Common stock issued under equity compensation plans, value		$ 1	3,983		3,984
Equity component of convertible senior notes			42,431		42,431
Purchase of capped calls related to convertible senior notes			(12,837)		(12,837)
Stock-based compensation expense			3,854		3,854
Net income				11,212	11,212
Ending balance, shares at Apr. 30, 2021		61,069
Ending balance, value at Apr. 30, 2021		$ 61	$ 637,534	$ (559,859)	$ 77,736