Pension Benefits (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Jan. 31, 2020	Apr. 30, 2019
Pension and Other Postretirement Benefits Cost (Reversal of Cost) [Abstract]
Pension contribution	$ 0.5	$ 7.3

Amount of contribution received by defined benefit plan from employer which increases plan assets.

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