Employees Benefit Plans - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 28, 2017	Oct. 29, 2016	Oct. 28, 2017	Oct. 29, 2016
BNC [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Company contributions, employee benefit expenses	$ 998	$ 991	$ 2,209	$ 2,240
MBS [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Company contributions, employee benefit expenses	$ 1		$ 2