Organization, Use of Estimates and Basis of Presentation - Summary of Potentially Antidilutive Securities (Details) - shares	6 Months Ended
	Oct. 31, 2018	Oct. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	4,345,096	4,499,214
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	2,466,877	2,494,930
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	1,878,219	2,004,284