Property, Plant and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 488,767	$ 462,943
Less accumulated amortization and depreciation	(284,943)	(254,680)
Property, Plant and Equipment, Net, Total	203,824	208,263
Amortization and depreciation expense on property, plant and equipment	36,900	36,200	$ 21,900
Accumulated amortization on capital leases	32,300	30,800
Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,431	4,751
Buildings And Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	120,819	114,421
Building And Improvements - Capital Leases [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	11,636	11,202
Machinery And Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	312,806	294,993
Machinery And Equipment - Capital Leases [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	30,911	30,574
Construction In Progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 8,164	$ 7,002