Summary of Significant Accounting Policies - Summary of Potentially Dilutive Stock-based Instruments (Details) - shares	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016
Class of Stock [Line Items]
Total common stock equivalents	4,312,988	4,322,597
Warrant
Class of Stock [Line Items]
Total common stock equivalents	2,004,284	2,109,840
Employee Stock Option
Class of Stock [Line Items]
Total common stock equivalents	2,308,704	2,212,757