Property, Plant and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
Apr. 30, 2021	Apr. 30, 2020	Apr. 30, 2019
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 501,596	$ 488,767
Less accumulated amortization and depreciation	(297,594)	(284,943)
Property, Plant and Equipment, Net, Total	204,002	203,824
Amortization and depreciation expense on property, plant and equipment	38,300	36,900	$ 36,200
Accumulated amortization on capital leases	33,000	32,300
Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,431	4,431
Buildings And Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	116,103	120,819
Building And Improvements - Capital Leases [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	11,636	11,636
Machinery And Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	315,371	312,806
Machinery And Equipment - Capital Leases [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	31,386	30,911
Construction In Progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 22,669	$ 8,164

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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- Definition

The total charge for the use of long-lived depreciable assets subject to a lease meeting the criteria for capitalization.

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Amount of expense charged against earnings to allocate the cost of tangible and intangible assets over their remaining economic lives, classified as other.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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