Segment Reporting - Information about Reportable Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 28, 2017	Jan. 30, 2016	Jan. 28, 2017	Jan. 30, 2016	Apr. 30, 2016
Segment Reporting Information [Line Items]
Net sales	$ 1,397,418	$ 1,400,853	$ 4,148,095	$ 3,932,933
Operating income (loss) from continuing operations	46,554	95,729	191,773	241,369
Total assets	3,594,062		3,594,062		$ 3,520,804
Operating Segments [Member] | Dental [Member]
Segment Reporting Information [Line Items]
Net sales	626,343	637,651	1,782,911	1,814,090
Operating income (loss) from continuing operations	40,018	82,108	177,356	223,454
Total assets	906,181		906,181		994,113
Operating Segments [Member] | Animal Health [Member]
Segment Reporting Information [Line Items]
Net sales	762,577	749,713	2,332,354	2,081,463
Operating income (loss) from continuing operations	23,777	25,959	60,460	64,108
Total assets	2,169,246		2,169,246		2,064,302
Operating Segments [Member] | Corporate [Member]
Segment Reporting Information [Line Items]
Net sales	8,498	13,489	32,830	37,380
Operating income (loss) from continuing operations	(17,241)	$ (12,338)	(46,043)	$ (46,193)
Total assets	$ 518,635		$ 518,635		$ 462,389