Segment Reporting - Information about Reportable Segments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Oct. 25, 2014	Oct. 26, 2013	Oct. 25, 2014	Oct. 26, 2013
Segment Reporting Information [Line Items]
Net sales	$ 1,103,325	$ 998,834	$ 2,162,854	$ 1,878,959
Operating income	91,221	75,223	175,975	156,504
Dental Supply [Member]
Segment Reporting Information [Line Items]
Net sales	601,748	563,052	1,154,402	1,117,285
Operating income	59,008	53,174	112,221	108,664
Veterinary Supply [Member]
Segment Reporting Information [Line Items]
Net sales	376,472	308,120	762,774	507,803
Operating income	14,336	12,151	28,323	21,198
Rehabilitation Supply [Member]
Segment Reporting Information [Line Items]
Net sales	125,105	127,662	245,678	253,871
Operating income	$ 17,877	$ 9,898	$ 35,431	$ 26,642