Fair Value Measurements - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Apr. 25, 2015	Apr. 19, 2014
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Long-lived assets	$ 5.6us-gaap_NoncurrentAssets	$ 0.9us-gaap_NoncurrentAssets
Significant unobservable inputs (Level 3) [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Long-lived assets measured fair value on nonrecurring basis	$ 3.2	$ 0

Long-lived assets other than financial instruments, long-term customer relationships of a financial institution, mortgage and other servicing rights, deferred policy acquisition costs, and deferred tax assets.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 280

-SubTopic 10

-Section 50

-Paragraph 41

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e9038-108599

Name:	us-gaap_NoncurrentAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant