Property, Plant and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 444,634	$ 324,007
Less accumulated amortization and depreciation	(226,532)	(216,074)
Property, Plant and Equipment, Net, Total	218,102	107,933
Amortization and depreciation expense on property, plant and equipment	21,900	14,200	$ 11,600
Accumulated amortization on capital leases	30,000	29,700
Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,751	3,581
Buildings And Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	112,757	81,172
Building And Improvements - Capital Leases [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	11,202	11,202
Machinery And Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	274,723	187,836
Machinery And Equipment - Capital Leases [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	30,270	29,378
Construction In Progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 10,931	$ 10,838

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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- Definition

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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