Assets held for sale (Details) (USD $) In Millions, unless otherwise specified	Dec. 26, 2014	Dec. 27, 2013
Discontinued Operations and Disposal Groups [Abstract]
Long-lived assets held for sale	$ 1.7	$ 1.9

Fair value portion of assets classified as held for sale.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19190-110258

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