Goodwill and Other Intangibles (Details)	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 25, 2016 USD ($) restaurant item	Dec. 27, 2015 USD ($)
Goodwill
Goodwill, Beginning Balance	$ 85,529,000	$ 79,657,000
Acquisitions		10,166,000
Divestitures		(2,481,000)
Adjustment to assets held for sale		979,000
Foreign currency adjustments	1,363,000	(2,792,000)
Goodwill, Ending Balance	86,892,000	85,529,000	$ 79,657,000
Goodwill impairment loss			0
Franchise Rights
Goodwill
Finite-lived intangible assets	1,800,000	2,400,000
Accumulated amortization	1,400,000	800,000
Amortization expense	600,000	400,000	200,000
Domestic Company-owned Restaurants
Goodwill
Goodwill, Beginning Balance	70,048,000	62,363,000
Acquisitions		10,166,000
Divestitures		(2,481,000)
Goodwill, Ending Balance	70,048,000	$ 70,048,000	62,363,000
Number of restaurants acquired | restaurant		25
Number of domestic markets in which restaurants acquired | item		4
Number of restaurants divested | restaurant		42
Number of domestic markets in which restaurants divested | item		1
International
Goodwill
Goodwill, Beginning Balance	15,045,000	$ 16,858,000
Adjustment to assets held for sale		979,000
Foreign currency adjustments	1,363,000	(2,792,000)
Goodwill, Ending Balance	16,408,000	15,045,000	16,858,000
Goodwill, accumulated impairment	2,300,000	2,300,000	2,300,000
All others
Goodwill
Goodwill, Beginning Balance	436,000	436,000
Goodwill, Ending Balance	$ 436,000	$ 436,000	$ 436,000