Retirement Plan (Details) - USD ($) $ in Millions	12 Months Ended
Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2017
Retirement Plan
Employee contributions matched by employer (as a percent)	50.00%
Employee compensation eligible for employer match of employee contributions (as a percent)	4.00%
Employer contributions to defined contribution retirement plan	$ 4.7	$ 4.3	$ 3.7

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

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