Organization, Use of Estimates and Basis of Presentation - Summary of Potentially Antidilutive Securities (Details) - shares	3 Months Ended
	Jul. 31, 2018	Jul. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	4,691,379	4,506,090
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	2,687,095	2,501,806
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	2,004,284	2,004,284