Share-Based Payments - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Jan. 31, 2021	Apr. 30, 2020
Total
Outstanding, beginning balance (in shares)	2,271,658
Granted (in shares)	133,833
Exercised (in shares)	(663,444)
Forfeited (in shares)	(7,000)
Canceled (in shares)	(35,901)
Expired (in shares)	(5,834)
Outstanding, ending balance (in shares)	1,693,312	2,271,658
Vested and expected to vest (in shares)	1,693,312
Exercisable (in shares)	1,298,688
Weighted Average Exercise Price
Outstanding, beginning balance (in usd per share)	$ 3.23
Granted (in usd per share)	9.21
Exercised (in usd per share)	2.27
Forfeited (in usd per share)	6.43
Canceled (in usd per share)	4.03
Expired (in usd per share)	10.80
Outstanding, ending balance (in usd per share)	4.02	$ 3.23
Vested and expected to vest (in usd per share)	4.02
Exercisable (in usd per share)	$ 3.25
Weighted Average Remaining Contractual Life (Years)
Outstanding (in years)	5 years 7 months 28 days	5 years
Outstanding, granted (in years)	7 years 6 months 29 days
Vested and expected to vest (in years)	5 years 7 months 28 days
Exercisable (in years)	4 years 11 months 4 days
Aggregate Intrinsic Value
Outstanding	$ 11,975	$ 10,663
Vested and expected to vest	11,975
Exercisable	$ 10,173
Directors and Employees
Total
Outstanding, beginning balance (in shares)	2,228,326
Granted (in shares)	133,833
Exercised (in shares)	(662,285)
Forfeited (in shares)	(7,000)
Canceled (in shares)	(34,978)
Expired (in shares)	0
Outstanding, ending balance (in shares)	1,657,896	2,228,326
Vested and expected to vest (in shares)	1,657,896
Exercisable (in shares)	1,289,104
Non- Employees
Total
Outstanding, beginning balance (in shares)	43,332
Granted (in shares)	0
Exercised (in shares)	(1,159)
Forfeited (in shares)	0
Canceled (in shares)	(923)
Expired (in shares)	(5,834)
Outstanding, ending balance (in shares)	35,416	43,332
Vested and expected to vest (in shares)	35,416
Exercisable (in shares)	9,584