12. Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended																12 Months Ended
		Apr. 30, 2021		Jan. 31, 2021		Oct. 31, 2020		Jul. 31, 2020		Apr. 30, 2020		Jan. 31, 2020		Oct. 31, 2019		Jul. 31, 2019		Apr. 30, 2021	Apr. 30, 2020	Apr. 30, 2019
Quarterly Financial Information Disclosure [Abstract]
Revenues		$ 27,606		$ 21,806		$ 21,064		$ 25,392		$ 12,550		$ 13,585		$ 18,313		$ 15,254
Gross profit (loss)		8,143		6,202		6,418		8,544		(1,299)		785		3,360		1,086		$ 29,307	$ 3,932	$ 7,224
Total operating expenses		5,055		4,018		4,166		3,825		3,528	[1]	2,996	[1]	3,889	[1]	4,459	[1]
Interest and other income (expense), net	[2]	(1,097)		23		32		11
Net (loss) income		1,991		2,207		2,284		4,730		(4,768)		(2,104)		(430)		(3,164)		11,212	(10,466)	(4,215)
Series E preferred stock accumulated dividends		(1,211)		(1,442)		(1,442)		(1,442)		(1,442)		(1,442)		(1,442)		(1,442)		(4,455)	(4,686)	(4,686)
Impact of Series E preferred stock redemption		(3,439)		0		0		0										$ (3,439)	$ 0	$ 0
Net income (loss) attributable to common stockholders		$ (2,659)		$ 765		$ 842		$ 3,288		$ (6,210)		$ (3,546)		$ (1,872)		$ (4,606)
Basic and diluted net income (loss) per common share attributable to common stockholders		$ (0.04)	[3]	$ 0.01	[3]	$ 0.01	[3]	$ 0.06	[3]	$ (0.11)	[3]	$ (0.06)	[3]	$ (0.03)	[3]	$ (0.08)	[3]	$ 0.06	$ (0.27)	$ (0.16)

[1] Total operating expenses for the second quarter of fiscal year ended April 30, 2020 includes a loss on lease termination of $0.4 million (Note 4).

[2] Interest and other income (expense), net, for the fourth quarter ended April 30, 2021 includes aggregate interest expense of $1.1 million related to our Convertible Notes issued in March 2021 (Note 3).

[3] Basic and diluted net income (loss) per common share attributable to common stockholders was the same for all periods presented.