Segment Reporting - Information about Reportable Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 30, 2016	Jan. 24, 2015	Jan. 30, 2016	Jan. 24, 2015	Apr. 25, 2015
Segment Reporting Information [Line Items]
Net sales	$ 1,400,853	$ 958,628	$ 3,932,933	$ 2,875,804
Operating income (loss) from continuing operations	95,729	77,377	241,369	215,513
Total assets, excluding assets held for sale	3,555,670		3,555,670		$ 2,193,565
Assets held for sale	0		0		754,141
Total assets	3,555,670		3,555,670		2,947,706
Corporate [Member]
Segment Reporting Information [Line Items]
Total assets, excluding assets held for sale	526,452		526,452		539,863
Dental [Member]
Segment Reporting Information [Line Items]
Total assets, excluding assets held for sale	935,347		935,347		1,022,257
Animal Health [Member]
Segment Reporting Information [Line Items]
Total assets, excluding assets held for sale	2,093,871		2,093,871		$ 631,445
Operating Segments [Member] | Corporate [Member]
Segment Reporting Information [Line Items]
Net sales	13,489	10,158	37,380	29,050
Operating income (loss) from continuing operations	(12,338)	(12,535)	(46,193)	(38,698)
Operating Segments [Member] | Dental [Member]
Segment Reporting Information [Line Items]
Net sales	637,651	610,655	1,814,090	1,746,165
Operating income (loss) from continuing operations	82,108	78,048	223,454	214,024
Operating Segments [Member] | Animal Health [Member]
Segment Reporting Information [Line Items]
Net sales	749,713	337,815	2,081,463	1,100,589
Operating income (loss) from continuing operations	$ 25,959	$ 11,864	$ 64,108	$ 40,187