Acquisitions - Additional Information (Detail) (National Veterinary Services Limited (NVS) [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
Oct. 25, 2014	Oct. 26, 2013	Oct. 25, 2014	Oct. 26, 2013
National Veterinary Services Limited (NVS) [Member]
Business Acquisition [Line Items]
Acquisition contributed of net sales	$ 173,946	$ 117,748	$ 347,522	$ 117,748

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration