Acquisitions - Summary of Acquired Intangible Assets Excluding Goodwill (Detail) - Animal Health International [Member] - USD ($) $ in Thousands	Jun. 16, 2015	Aug. 01, 2015
Business Acquisition [Line Items]
Total amortized intangible assets	$ 422,000
Total identifiable intangible assets	$ 434,300	$ 434,300
Finite lived intangible assets, Weighted average life (years)	13 years 7 months 6 days
Unamortized Trade Names [Member]
Business Acquisition [Line Items]
Unamortized - indefinite lived	$ 12,300
Indefinite lived intangible assets, Weighted average life (years)	indefinite
Customer Relationships [Member]
Business Acquisition [Line Items]
Total amortized intangible assets	$ 291,900
Finite lived intangible assets, Weighted average life (years)	15 years
Amortized Trade Names [Member]
Business Acquisition [Line Items]
Total amortized intangible assets	$ 111,400
Finite lived intangible assets, Weighted average life (years)	10 years
Developed Technology and Other [Member]
Business Acquisition [Line Items]
Total amortized intangible assets	$ 18,700
Finite lived intangible assets, Weighted average life (years)	12 years 2 months 12 days