Pension Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 28, 2017	Oct. 29, 2016	Oct. 28, 2017	Oct. 29, 2016
Net periodic pension costs
Service cost	$ 329	$ 319	$ 658	$ 638
Interest cost	1,147	1,170	2,294	2,340
Expected return on plan assets	(1,204)	(1,245)	(2,408)	(2,490)
Net amortization	780	764	1,560	1,528
Net periodic pension cost	$ 1,052	$ 1,008	$ 2,104	$ 2,016