Property, Plant and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended
	Jul. 31, 2022	Jul. 31, 2021	Apr. 30, 2022
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 543,742		$ 541,328
Less accumulated amortization and depreciation	(336,554)		(327,520)
Property, Plant and Equipment, Net, Total	207,188		213,808
Amortization and depreciation expense on property, plant and equipment	9,700	$ 9,600
Finance lease, right-of-use asset, accumulated amortization	33,200		32,800
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,431		4,431
Buildings and improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	119,384		119,066
Buildings and improvements - finance leases
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	11,164		11,164
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	326,656		324,417
Machinery and equipment - finance leases
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	31,546		31,341
Software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	27,816		28,115
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 22,745		$ 22,794