Segment Reporting - Information about Reportable Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 27, 2018	Oct. 28, 2017	Oct. 27, 2018	Oct. 28, 2017	Apr. 28, 2018
Segment Reporting Information [Line Items]
Net sales	$ 1,404,752	$ 1,385,737	$ 2,741,072	$ 2,689,852
Operating income (loss)	41,216	71,759	45,730	128,592
Total assets	3,344,254		3,344,254		$ 3,471,664
Consumable
Segment Reporting Information [Line Items]
Net sales	1,138,251	1,116,091	2,247,648	2,196,196
Equipment and software
Segment Reporting Information [Line Items]
Net sales	182,120	181,337	329,018	318,286
Other
Segment Reporting Information [Line Items]
Net sales	84,381	88,309	164,406	175,370
Dental
Segment Reporting Information [Line Items]
Net sales	542,516	553,630	1,048,580	1,072,437
Dental | Operating Segments
Segment Reporting Information [Line Items]
Operating income (loss)	41,594	65,207	77,467	124,726
Total assets	668,603		668,603		853,555
Dental | Consumable
Segment Reporting Information [Line Items]
Net sales	303,806	311,217	608,045	631,395
Dental | Equipment and software
Segment Reporting Information [Line Items]
Net sales	167,686	169,513	302,643	297,376
Dental | Other
Segment Reporting Information [Line Items]
Net sales	71,024	72,900	137,892	143,666
Animal Health
Segment Reporting Information [Line Items]
Net sales	855,408	823,583	1,680,622	1,599,719
Animal Health | Operating Segments
Segment Reporting Information [Line Items]
Operating income (loss)	22,031	23,217	41,063	39,893
Total assets	2,158,144		2,158,144		2,128,800
Animal Health | Consumable
Segment Reporting Information [Line Items]
Net sales	834,445	804,874	1,639,603	1,564,801
Animal Health | Equipment and software
Segment Reporting Information [Line Items]
Net sales	14,434	11,824	26,375	20,910
Animal Health | Other
Segment Reporting Information [Line Items]
Net sales	6,529	6,885	14,644	14,008
Corporate
Segment Reporting Information [Line Items]
Net sales	6,828	8,524	11,870	17,696
Corporate | Operating Segments
Segment Reporting Information [Line Items]
Operating income (loss)	(22,409)	(16,665)	(72,800)	(36,027)
Total assets	517,507		517,507		$ 489,309
Corporate | Other
Segment Reporting Information [Line Items]
Net sales	6,828	8,524	11,870	17,696
United States
Segment Reporting Information [Line Items]
Net sales	1,173,623	1,151,380	2,270,087	2,231,707
United States | Dental
Segment Reporting Information [Line Items]
Net sales	495,457	500,803	949,030	967,491
United States | Animal Health
Segment Reporting Information [Line Items]
Net sales	671,338	642,053	1,309,187	1,246,520
United States | Corporate
Segment Reporting Information [Line Items]
Net sales	6,828	8,524	11,870	17,696
United Kingdom
Segment Reporting Information [Line Items]
Net sales	150,452	148,734	304,357	289,588
United Kingdom | Animal Health
Segment Reporting Information [Line Items]
Net sales	150,452	148,734	304,357	289,588
Canada
Segment Reporting Information [Line Items]
Net sales	80,677	85,623	166,628	168,557
Canada | Dental
Segment Reporting Information [Line Items]
Net sales	47,059	52,827	99,550	104,946
Canada | Animal Health
Segment Reporting Information [Line Items]
Net sales	$ 33,618	$ 32,796	$ 67,078	$ 63,611