Significant Accounting Policies - Summary of Potentially Antidilutive Securities (Details) - shares	3 Months Ended
	Jul. 31, 2019	Jul. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	4,044,648	4,691,379
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	2,374,875	2,687,095
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	1,669,773	2,004,284