Description of Business and Summary of Significant Accounting Policies - Schedule of continuing franchise royalties and miscellaneous fees (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Jan. 01, 2017	Jan. 03, 2016
Franchisor Disclosure [Line Items]
Advertising contributions from franchisees	$ 2.1	$ 2.2	$ 2.1

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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