Significant Accounting Policies - Fiscal Year, Revenue Recognition and Advertising Costs (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 25, 2016	Dec. 27, 2015
Significant accounting policies
Length of fiscal year	371 days	364 days	364 days
Advertising and related costs	$ 72.3	$ 70.9	$ 67.2
Maximum
Significant accounting policies
Amortization term of equipment incentives	3 years

Expenditures for planning and executing the conception, pricing, promotion, and distribution of ideas, goods, and services. Costs of public relations and corporate promotions are typically considered to be marketing costs.

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 210.5-03.4)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Name:	us-gaap_MarketingExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration