Segment Reporting - Sales Information by Product (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 28, 2017	Jan. 30, 2016	Jan. 28, 2017	Jan. 30, 2016
Segment Reporting Information [Line Items]
Net sales	$ 1,397,418	$ 1,400,853	$ 4,148,095	$ 3,932,933
Consumable [Member]
Segment Reporting Information [Line Items]
Net sales	1,064,098	1,059,838	3,252,551	3,042,634
Equipment and Software [Member]
Segment Reporting Information [Line Items]
Net sales	249,047	248,779	627,187	610,071
Other [Member]
Segment Reporting Information [Line Items]
Net sales	$ 84,273	$ 92,236	$ 268,357	$ 280,228