Acquisitions - Summary of Total Purchase Price Consideration and Preliminary Fair Value of Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Thousands	Jun. 16, 2015	Aug. 01, 2015	Apr. 25, 2015
Business Acquisition [Line Items]
Goodwill		$ 817,481	$ 299,924
Animal Health International [Member]
Business Acquisition [Line Items]
Cash	$ 1,100,000
Net working capital adjustment	7,704
Fair value of total purchase price consideration	1,107,704
Receivables	161,427
Inventory	195,367
Prepaid expenses and other current assets	33,005
Property and equipment	44,178
Identifiable intangibles	434,300
Other long-term assets	40,869
Total assets acquired	909,146
Accounts payable	122,129
Accrued liabilities and other current liabilities	19,395
Deferred tax liability	177,789
Total liabilities assumed	319,313
Identifiable net assets acquired	589,833
Goodwill	517,871
Net assets acquired	$ 1,107,704