Significant Accounting Policies - Summary of Potentially Antidilutive Securities (Details) - shares	9 Months Ended
	Jan. 31, 2021	Jan. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents (in shares)	1,693,312	4,036,371
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents (in shares)	1,693,312	2,366,598
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total common stock equivalents (in shares)	0	1,669,773