Acquisitions and Divestitures - Assets Held for Sale (Details) $ in Thousands		1 Months Ended	12 Months Ended
	Feb. 26, 2018 USD ($) restaurant	Sep. 30, 2015 restaurant	Dec. 31, 2017 USD ($)	Dec. 25, 2016 USD ($)
Assets Held for Sale disclosures
Impairment loss			$ 1,674	$ 1,350
Assets classified as held for sale
Cash			908
Inventories			505	621
Prepaid expenses			570	517
Net property and equipment			4,878	4,767
Other assets			946	568
Valuation allowance			(1,674)	(216)
Total assets held for sale			6,133	6,257
Liabilities classified as held for sale
Accounts payable			1,817
Accrued and other liabilities			470
Total liabilities held for sale			2,287
China Operations
Assets Held for Sale disclosures
Number of restaurants expected to be sold | restaurant		35
Impairment loss			$ 1,700	$ 1,400
Stores in Denver, Colorado market
Liabilities classified as held for sale
Ownership share in stores being refranchised (as a percent)			60.00%
Stores in Denver, Colorado market | Subsequent event
Liabilities classified as held for sale
Number of restaurants divested | restaurant	31
Sale price	$ 4,500