Organization, Use of Estimates and Basis of Presentation - Narrative (Details)	3 Months Ended		6 Months Ended
	Oct. 31, 2017 USD ($)	Oct. 31, 2016 USD ($)	Oct. 31, 2017 USD ($) subsidiary	Oct. 31, 2016 USD ($)	Oct. 30, 2017 USD ($)	Apr. 30, 2017 USD ($)	Apr. 30, 2016 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of operating subsidiaries | subsidiary			2
Net loss	$ (94,318)	$ (504,000)	$ (768,475)	$ (3,051,000)
Net cash used in operating activities			1,680,000	2,555,000
Positive working capital	0		0
Cash and cash equivalents	660,000	4,328,000	660,000	4,328,000		$ 3,295,000	$ 2,585,000
Investment in new lab equipment			910,000
Capitalized, non-recurring costs			100,000
Credit facility					$ 1,500,000.0
Unrecognized tax benefits	121,000		121,000			$ 121,000
Provision for (Benefit from) income taxes	$ 11,000	$ (5,000)	$ 15,000	$ 9,000