Segment Reporting - Information about Reportable Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 26, 2019	Jan. 27, 2018	Jan. 26, 2019	Jan. 27, 2018	Apr. 28, 2018
Segment Reporting Information [Line Items]
Net sales	$ 1,396,745	$ 1,375,222	$ 4,137,817	$ 4,065,074
Operating income (loss)	45,363	50,046	91,093	178,638
Total assets	3,320,525		3,320,525		$ 3,471,664
Consumable
Segment Reporting Information [Line Items]
Net sales	1,079,566	1,074,189	3,327,214	3,270,385
Equipment and software
Segment Reporting Information [Line Items]
Net sales	234,251	222,574	563,269	540,860
Other
Segment Reporting Information [Line Items]
Net sales	82,928	78,459	247,334	253,829
Dental
Segment Reporting Information [Line Items]
Net sales	579,733	577,877	1,628,313	1,650,314
Dental | Operating Segments
Segment Reporting Information [Line Items]
Operating income (loss)	51,120	58,439	128,587	183,165
Total assets	679,790		679,790		853,555
Dental | Consumable
Segment Reporting Information [Line Items]
Net sales	294,708	302,296	902,753	933,691
Dental | Equipment and software
Segment Reporting Information [Line Items]
Net sales	217,649	207,000	520,292	504,376
Dental | Other
Segment Reporting Information [Line Items]
Net sales	67,376	68,581	205,268	212,247
Animal Health
Segment Reporting Information [Line Items]
Net sales	807,495	794,867	2,488,117	2,394,586
Animal Health | Operating Segments
Segment Reporting Information [Line Items]
Operating income (loss)	15,033	18,037	56,096	57,930
Total assets	2,172,044		2,172,044		2,128,800
Animal Health | Consumable
Segment Reporting Information [Line Items]
Net sales	784,858	771,893	2,424,461	2,336,694
Animal Health | Equipment and software
Segment Reporting Information [Line Items]
Net sales	16,602	15,574	42,977	36,484
Animal Health | Other
Segment Reporting Information [Line Items]
Net sales	6,035	7,400	20,679	21,408
Corporate
Segment Reporting Information [Line Items]
Net sales	9,517	2,478	21,387	20,174
Corporate | Operating Segments
Segment Reporting Information [Line Items]
Operating income (loss)	(20,790)	(26,430)	(93,590)	(62,457)
Total assets	468,691		468,691		$ 489,309
Corporate | Other
Segment Reporting Information [Line Items]
Net sales	9,517	2,478	21,387	20,174
United States
Segment Reporting Information [Line Items]
Net sales	1,170,446	1,150,650	3,440,533	3,382,357
United States | Dental
Segment Reporting Information [Line Items]
Net sales	529,522	525,934	1,478,552	1,493,425
United States | Animal Health
Segment Reporting Information [Line Items]
Net sales	631,407	622,238	1,940,594	1,868,758
United States | Corporate
Segment Reporting Information [Line Items]
Net sales	9,517	2,478	21,387	20,174
United Kingdom
Segment Reporting Information [Line Items]
Net sales	141,877	137,404	446,234	426,992
United Kingdom | Animal Health
Segment Reporting Information [Line Items]
Net sales	141,877	137,404	446,234	426,992
Canada
Segment Reporting Information [Line Items]
Net sales	84,422	87,168	251,050	255,725
Canada | Dental
Segment Reporting Information [Line Items]
Net sales	50,211	51,943	149,761	156,889
Canada | Animal Health
Segment Reporting Information [Line Items]
Net sales	$ 34,211	$ 35,225	$ 101,289	$ 98,836