Share-Based Payments - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Oct. 31, 2020	Apr. 30, 2020
Total
Outstanding, beginning balance (in shares)	2,271,658
Granted (in shares)	60,000
Exercised (in shares)	(641,817)
Forfeited (in shares)	(5,500)
Canceled (in shares)	(27,029)
Expired (in shares)	(5,834)
Outstanding, ending balance (in shares)	1,651,478	2,271,658
Vested and expected to vest (in shares)	1,651,478
Exercisable (in shares)	1,312,980
Weighted Average Exercise Price
Outstanding, beginning balance (in usd per share)	$ 3.23
Granted (in usd per share)	7.29
Exercised (in usd per share)	2.24
Forfeited (in usd per share)	6.76
Canceled (in usd per share)	4.00
Expired (in usd per share)	10.80
Outstanding, ending balance (in usd per share)	3.71	$ 3.23
Vested and expected to vest (in usd per share)	3.71
Exercisable (in usd per share)	$ 3.15
Weighted Average Remaining Contractual Life (Years)
Weighted Average Remaining Contractual Term, Outstanding (in years)	5 years 9 months 29 days	5 years
Weighted Average Remaining Contractual Term, Outstanding, Granted (in years)	9 years 10 months 2 days
Weighted Average Remaining Contractual Life, Vested and expected to vest (in years)	5 years 9 months 29 days
Weighted Average Remaining Contractual Life, Exercisable (in years)	5 years 1 month 13 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value, Outstanding	$ 8,641	$ 10,663
Aggregate Intrinsic Value, Vested and expected to vest	8,641
Aggregate Intrinsic Value, Exercisable	$ 7,660
Directors and Employees
Total
Outstanding, beginning balance (in shares)	2,228,326
Granted (in shares)	60,000
Exercised (in shares)	(640,657)
Forfeited (in shares)	(5,500)
Canceled (in shares)	(26,106)
Expired (in shares)	0
Outstanding, ending balance (in shares)	1,616,063	2,228,326
Vested and expected to vest (in shares)	1,616,063
Exercisable (in shares)	1,303,396
Non- Employees
Total
Outstanding, beginning balance (in shares)	43,332
Granted (in shares)	0
Exercised (in shares)	(1,160)
Forfeited (in shares)	0
Canceled (in shares)	(923)
Expired (in shares)	(5,834)
Outstanding, ending balance (in shares)	35,415	43,332
Vested and expected to vest (in shares)	35,415
Exercisable (in shares)	9,584