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Name:	us-gaap_DefinedContributionPlanDisclosureLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Defined Contribution Plans - Additional Information (Detail) - USD ($)	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
U.S. Employees 401(K) Plan [Member] \| Maximum [Member]
Defined Contribution Plan Disclosure [Line Items]
Percentage of employee contributions matched to the plan	4.00%
U.K. Employees Personal Pension Plan and U.S. Employees 401(K) Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Total employer contributions	$ 314,000	$ 237,000	$ 219,000