Significant Accounting Policies - Summary of Potentially Antidilutive Securities (Details) - shares	9 Months Ended
	Jan. 31, 2019	Jan. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	4,161,608	4,523,129
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	2,490,168	2,518,845
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	1,671,440	2,004,284