Significant Accounting Policies - Summary of Potentially Antidilutive Securities (Details) - shares	6 Months Ended
	Oct. 31, 2019	Oct. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	4,123,647	4,345,096
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	2,453,874	2,466,877
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	1,669,773	1,878,219