11. Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended																12 Months Ended
		Apr. 30, 2019		Jan. 31, 2019		Oct. 31, 2018		Jul. 31, 2018		Apr. 30, 2018		Jan. 31, 2018		Oct. 31, 2017		Jul. 31, 2017		Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2017
Quarterly Financial Information Disclosure [Abstract]
Revenues	[1]	$ 17,055		$ 13,781		$ 10,178		$ 12,589		$ 6,943		$ 6,819		$ 12,782		$ 27,077
Gross profit		3,648	[1]	2,050	[1]	334	[1]	1,192	[1]	(1,961)	[1]	(4,132)	[1]	(3,460)	[1]	6,629	[1]	$ 7,224	$ (2,924)	$ 19,371
Income (loss) from continuing operations	[1]	234		(1,139)		(2,190)		(1,961)		(6,134)		(8,928)		(8,301)		2,800
Income (loss) from discontinued operations		102	[1],[2],[3]	0	[1],[2],[3]	739	[1],[2],[3]	0	[1],[2],[3]	9,154	[1],[2],[3]	(2,076)	[1],[2],[3]	(4,323)	[1],[2],[3]	(4,005)	[1],[2],[3]	841	(1,250)	(29,552)
Net income (loss)		336	[1]	(1,139)	[1]	(1,451)	[1]	(1,961)	[1]	3,020	[1]	(11,004)	[1]	(12,624)	[1]	(1,205)	[1]	(4,215)	(21,813)	(28,159)
Net income (loss) attributable to common stockholders		$ (1,106)	[1]	$ (2,581)	[1]	$ (2,893)	[1]	$ (3,403)	[1]	$ 1,578	[1]	$ (12,446)	[1]	$ (14,066)	[1]	$ (2,647)	[1]	$ (8,901)	$ (26,499)	$ (32,799)
Basic and diluted net income (loss) per common share attributable to common stockholders - Continuing operations		$ (0.02)	[4]	$ (0.05)	[4]	$ (0.06)	[4]	$ (0.06)	[4]	$ (0.14)	[4]	$ (0.23)	[4]	$ (0.21)	[4]	$ 0.03	[4]	$ (0.17)	$ (0.53)	$ (0.09)
Basic and diluted net income (loss) per common share attributable to common stockholders - Discontinued operations						0.01				0.17		(0.05)		(0.10)		(0.09)		0.01	(0.03)	(0.79)
Net loss per share attributable to common stockholders		$ (0.02)		$ (0.05)		$ (0.05)		$ (0.05)		$ 0.03		$ (0.28)		$ (0.31)		$ (0.06)		$ (0.16)	$ (0.56)	$ (0.88)

[1] On May 1, 2018, we adopted ASC 606 using the modified retrospective method applied to all contracts not completed as of May 1, 2018 (Note 2). Under the modified retrospective method, results for the reporting periods beginning on or after May 1, 2018 are presented in accordance with ASC 606, while prior period amounts are not adjusted and continue to be reported under the accounting standards that were in effect prior to May 1, 2018.

[2] For all periods presented, the operating results of our former research and development segment are reported as income (loss) from discontinued operations, net of tax (Note 1).

[3] Income from discontinued operations, net of tax, for the quarters ended October 31, 2018 and April 30, 2018 include a gain on sale of research and development assets before tax of $1,000 and $8,000, respectively (Note 10).

[4] Basic and diluted net income (loss) per common share attributable to common stockholders calculations for each of the quarters are based on the basic and diluted weighted average common shares outstanding for each period. As such, the sum of the quarters may not necessarily equal the basic and diluted net income (loss) per common share amount for the fiscal year.