Organization, Use of Estimates and Basis of Presentation - Summary of Potentially Antidilutive Securities (Details) - shares	6 Months Ended
	Oct. 31, 2017	Oct. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	4,499,214	4,559,593
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	2,494,930	2,449,753
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	2,004,284	2,109,840