Organization, Use of Estimates and Basis of Presentation - Summary of Potentially Antidilutive Securities (Details) - shares	9 Months Ended
	Jan. 31, 2018	Jan. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	4,523,129	4,418,544
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	2,518,845	2,308,704
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	2,004,284	2,109,840