Segment Reporting (Company's Reportable Segments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Oct. 29, 2011	Oct. 30, 2010	Oct. 29, 2011	Oct. 30, 2010
Segment Reporting Information [Line Items]
Net sales	$ 856,875	$ 857,414	$ 1,704,297	$ 1,707,201
Operating income	83,259	90,152	165,252	179,176
Dental Supply [Member]
Segment Reporting Information [Line Items]
Net sales	550,605	563,210	1,083,972	1,105,888
Operating income	56,408	63,589	109,869	124,552
Rehabilitation Supply [Member]
Segment Reporting Information [Line Items]
Net sales	133,570	132,626	268,022	260,100
Operating income	18,807	18,302	36,577	35,535
Veterinary Supply [Member]
Segment Reporting Information [Line Items]
Net sales	172,700	161,578	352,303	341,213
Operating income	$ 8,044	$ 8,261	$ 18,806	$ 19,089