Significant Accounting Policies - Summary of Potentially Antidilutive Securities (Details) - shares	9 Months Ended
	Jan. 31, 2020	Jan. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	4,036,371	4,161,608
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	2,366,598	2,490,168
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents	1,669,773	1,671,440