Employee Savings Plan (Details) - USD ($)	12 Months Ended
Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
Employee Savings Plan
Amount of expense in contribution to the plan	$ 4,744,000	$ 3,961,000	$ 2,953,000

Amount of cost for defined contribution plan.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

Name:	us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration