Accumulated Other Comprehensive Loss, Reclassification out of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2021	Jan. 31, 2020	Jan. 31, 2021	Jan. 31, 2020
Amortization from Accumulated Other Comprehensive Loss [Abstract]
Pension expense	$ (3,012)	$ (2,410)	$ (8,257)	$ (5,711)
Reclassification out of Accumulated Other Comprehensive Loss [Member]
Amortization from Accumulated Other Comprehensive Loss [Abstract]
Pension expense	$ 1,900	$ 1,600	$ 5,800	$ 4,600