Organization, Use of Estimates and Basis of Presentation - Narrative (Details)	3 Months Ended		9 Months Ended
	Jan. 31, 2018 USD ($)	Jan. 31, 2017 USD ($)	Jan. 31, 2018 USD ($) subsidiary	Jan. 31, 2017 USD ($)	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	$ (76,000)	$ (1,408,904)	$ (844,000)	$ (4,459,773)
Net cash used in operating activities			1,235,000	3,238,000
Positive working capital	2,000,000		2,000,000
Cash and cash equivalents	1,062,000	3,488,000	1,062,000	3,488,000		$ 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 income taxes	$ 2,000	$ 0	18,000	$ 7,000
Reduction of federal and state deferred tax assets			$ 7,000,000