Accumulated Other Comprehensive Loss, Reclassification out of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2020	Oct. 31, 2019
Amortization from Accumulated Other Comprehensive Loss [Abstract]
Pension expense	$ (2,683)	$ (881)	$ (5,245)	$ (3,301)
Reclassification out of Accumulated Other Comprehensive Loss [Member]
Amortization from Accumulated Other Comprehensive Loss [Abstract]
Pension expense	$ 2,000	$ 1,700	$ 3,900	$ 3,000

Amount of net periodic benefit cost (credit) for defined benefit plan.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
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Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
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-Section 55
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-URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Name:	us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration