Segment Reporting - Sales Information by Product (Detail) - USD ($) $ in Thousands	3 Months Ended
	Jul. 29, 2017	Jul. 30, 2016
Segment Reporting Information [Line Items]
Net sales	$ 1,304,115	$ 1,332,436
Consumable
Segment Reporting Information [Line Items]
Net sales	1,080,105	1,076,221
Equipment and Software
Segment Reporting Information [Line Items]
Net sales	136,949	160,946
Other
Segment Reporting Information [Line Items]
Net sales	$ 87,061	$ 95,269