Information about Reportable Segments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Jan. 26, 2013	Jan. 28, 2012	Jan. 26, 2013	Jan. 28, 2012
Segment Reporting Information [Line Items]
Net sales	$ 915,861	$ 895,030	$ 2,672,279	$ 2,599,327
Operating income	89,538	89,906	249,999	255,158
Dental Supply
Segment Reporting Information [Line Items]
Net sales	626,494	605,041	1,743,035	1,689,013
Operating income	66,049	67,064	172,670	176,933
Veterinary Supply
Segment Reporting Information [Line Items]
Net sales	175,408	174,643	550,873	526,946
Operating income	9,942	7,983	29,380	26,789
Rehabilitation Supply
Segment Reporting Information [Line Items]
Net sales	113,959	115,346	378,371	383,368
Operating income	$ 13,547	$ 14,859	$ 47,949	$ 51,436