Pension Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 24, 2015	Oct. 25, 2014	Oct. 24, 2015	Oct. 25, 2014
Components of net periodic pension cost
Service cost	$ 333	$ 279	$ 666	$ 558
Interest cost	1,211	1,267	2,422	2,534
Expected return on plan assets	(1,226)	(1,269)	(2,452)	(2,538)
Net amortization	736	665	1,472	1,330
Net periodic pension cost	$ 1,054	$ 942	$ 2,108	$ 1,884