Pension Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 27, 2018	Oct. 28, 2017	Oct. 27, 2018	Oct. 28, 2017
Net periodic pension costs
Service cost	$ 323	$ 329	$ 646	$ 658
Interest cost	1,116	1,147	2,232	2,294
Expected return on plan assets	(1,136)	(1,204)	(2,272)	(2,408)
Net amortization	639	780	1,278	1,560
Net periodic pension cost	$ 942	$ 1,052	$ 1,884	$ 2,104