Stock-based Payments - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Apr. 30, 2021	Apr. 30, 2020	Apr. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, Beginning Balance (in shares)	2,271,658	2,423,626
Granted (in shares)	135,834	229,833
Exercised (in shares)	(687,338)	(248,495)
Canceled (in shares)	(48,674)	(11,824)
Forfeited (in shares)	(12,000)	(44,813)
Expired (in shares)	(5,834)	(76,669)
Outstanding, Ending Balance (in shares)	1,653,646	2,271,658	2,423,626
Vested and expected to vest (in shares)	1,653,646	2,271,658
Vested (in shares)	1,332,854	1,943,618
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted Average Exercise Price, Outstanding, Beginning Balance (in usd per share)	$ 3.23	$ 3.19
Weighted Average Exercise Price, Granted (in usd per share)	9.24	5.33
Weighted Average Exercise Price, Exercised (in usd per share)	2.33	2.31
Weighted Average Exercise Price, Canceled (in usd per share)	6.03	7.96
Weighted Average Exercise Price, Forfeited (in usd per share)	7.48	7.85
Weighted Average Exercise Price, Expired (in usd per share)	10.80	8.04
Weighted Average Exercise Price, Outstanding, Ending Balance (in usd per share)	3.96	3.23	$ 3.19
Weighted Average Exercise Price, Vested and Expected to Vest (in usd per share)	3.96	3.23
Weighted Average Exercise Price, Vested (in usd per share)	$ 3.34	$ 2.83
Weighted Average Remaining Contractual Term, Outstanding, Beginning Balance (in years)		5 years	5 years 3 months 18 days
Weighted Average Remaining Contractual Life, Granted	7 years 3 months 18 days	8 years 1 month 6 days
Weighted Average Remaining Contractual Term, Outstanding, Ending Balance (in years)	5 years 4 months 24 days	5 years
Weighted Average Remaining Contractual Life (Years), Vested and expected to vest	5 years 4 months 24 days	5 years
Weighted Average Remaining Contractual Life (Years), Vested	4 years 9 months 18 days	4 years 6 months
Aggregate Intrinsic Value, Outstanding, Beginning Balance	$ 10,663	$ 14,557
Aggregate Intrinsic Value, Granted	259	544
Aggregate Intrinsic Value, Outstanding, Ending Balance	11,384	10,663	$ 14,557
Aggregate Intrinsic Value, Vested and expected to vest	11,384	10,663
Aggregate Intrinsic Value, Vested	$ 9,995	$ 9,898
Non- Employees
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, Beginning Balance (in shares)	43,332	50,000
Granted (in shares)	0	0
Exercised (in shares)	(1,160)	0
Canceled (in shares)	(923)	0
Forfeited (in shares)	0	0
Expired (in shares)	(5,834)	(6,668)
Outstanding, Ending Balance (in shares)	35,415	43,332	50,000
Vested and expected to vest (in shares)	35,415	43,332
Vested (in shares)	9,584	17,501
Directors and Employees
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, Beginning Balance (in shares)	2,228,326	2,373,626
Granted (in shares)	135,834	229,833
Exercised (in shares)	(686,178)	(248,495)
Canceled (in shares)	(47,751)	(11,824)
Forfeited (in shares)	(12,000)	(44,813)
Expired (in shares)	0	(70,001)
Outstanding, Ending Balance (in shares)	1,618,231	2,228,326	2,373,626
Vested and expected to vest (in shares)	1,618,231	2,228,326
Vested (in shares)	1,323,270	1,926,117