Summary of Significant Accounting Policies - Summary of Potentially Dilutive Stock-based Instruments (Details) - shares	12 Months Ended
	Apr. 30, 2018	Apr. 30, 2017
Class of Stock [Line Items]
Total common stock equivalents	4,710,129	4,312,988
Warrant
Class of Stock [Line Items]
Total common stock equivalents	2,004,284	2,004,284
Employee Stock Option
Class of Stock [Line Items]
Total common stock equivalents	2,705,845	2,308,704