Information about Reportable Segments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Apr. 28, 2012	Jan. 28, 2012	Oct. 29, 2011	Jul. 30, 2011	Apr. 30, 2011	Jan. 29, 2011	Oct. 30, 2010	Jul. 31, 2010	Apr. 28, 2012	Apr. 30, 2011	Apr. 24, 2010
Segment Reporting Information [Line Items]
Net sales	$ 936,334	$ 895,030	$ 856,875	$ 847,422	$ 883,819	$ 824,650	$ 857,414	$ 849,787	$ 3,535,661	$ 3,415,670	$ 3,237,376
Operating income	102,851	89,906	83,259	81,993	104,125	92,707	90,152	89,024	358,009	376,008	355,291
Depreciation and amortization									42,209	41,339	39,474
Total assets	2,739,368				2,564,968				2,739,368	2,564,968	2,422,969
Dental Supply
Segment Reporting Information [Line Items]
Net sales									2,287,875	2,236,056	2,167,495
Operating income									246,755	272,185	263,750
Depreciation and amortization									31,375	27,410	26,277
Total assets	1,502,672				1,359,659				1,502,672	1,359,659	1,331,510
Rehabilitation Supply
Segment Reporting Information [Line Items]
Net sales									513,340	504,734	426,297
Operating income									72,442	66,809	59,922
Depreciation and amortization									7,472	7,833	5,909
Total assets	883,287				863,930				883,287	863,930	773,732
Veterinary Supply
Segment Reporting Information [Line Items]
Net sales									734,446	674,880	643,584
Operating income									38,812	37,014	31,619
Depreciation and amortization									3,362	6,096	7,288
Total assets	$ 353,409				$ 341,379				$ 353,409	$ 341,379	$ 317,727