Quarterly Data - Unaudited, in Thousands, except Per Share Data (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2017 USD ($) item $ / shares	Sep. 24, 2017 USD ($) item $ / shares	Jun. 25, 2017 USD ($) item $ / shares	Mar. 26, 2017 USD ($) item $ / shares	Dec. 25, 2016 USD ($) $ / shares	Sep. 25, 2016 USD ($) $ / shares	Jun. 26, 2016 USD ($) $ / shares	Mar. 27, 2016 USD ($) $ / shares	Dec. 31, 2017 USD ($) $ / shares	Dec. 25, 2016 USD ($) item $ / shares	Dec. 27, 2015 USD ($) $ / shares
Quarterly Financial Information
Total revenues | $	$ 467,606,000	$ 431,709,000	$ 434,778,000	$ 449,266,000	$ 439,619,000	$ 422,442,000	$ 422,964,000	$ 428,595,000	$ 1,783,359,000	$ 1,713,620,000	$ 1,637,375,000
Operating income | $	36,604,000	33,515,000	37,217,000	43,681,000	51,411,000	33,383,000	36,831,000	42,898,000	151,017,000	164,523,000	136,307,000
Net income attributable to the Company | $	$ 28,509,000	$ 21,817,000	$ 23,538,000	$ 28,428,000	$ 32,630,000	$ 21,467,000	$ 22,541,000	$ 26,182,000	$ 102,292,000	$ 102,820,000	$ 75,682,000
Basic earnings per common share | $ / shares	$ 0.82	$ 0.61	$ 0.66	$ 0.78	$ 0.89	$ 0.57	$ 0.61	$ 0.69	$ 2.86	$ 2.76	$ 1.91
Diluted earnings per common share | $ / shares	0.81	0.60	0.65	0.77	0.88	0.57	0.61	0.69	2.83	2.74	1.89
Dividends declared per common share | $ / shares	$ 0.225	$ 0.225	$ 0.200	$ 0.200	$ 0.200	$ 0.200	$ 0.175	$ 0.175	$ 0.85	$ 0.75	$ 0.63
Provisional one-time Tax Act tax benefit from remeasurement of deferred tax assets, liabilities and related valuation allowances | $	$ 7,000,000								$ 7,020,000
Provisional one-time Tax Act benefit, impact on basic and diluted EPS (in dollars per share) | $ / shares	$ 0.20
After income tax benefit from a 14th week of operation | $	$ 3,900,000
Favorable impact on diluted EPS from a 14th week of operations (in dollars per share) | $ / shares	$ 0.11
After tax gain from the sale of a domestic Company-owned market to a franchisee | $					$ 7,300,000
Impact on basic and diluted EPS from the sale of a domestic Company-owned market to a franchisee | $ / shares					$ 0.19
After tax gain related to a legal settlement | $					$ 600,000
Favorable impact on basic and diluted EPS related to a legal settlement | $ / shares					$ 0.02
Number of weeks in quarter | item	14	13	13	13						13
China Operations
Quarterly Financial Information
After tax loss from impairment related to company-owned stores in China currently for sale | $	$ 1,300,000				$ 900,000
Unfavorable impact on basic and diluted EPS from impairment related to Company-owned stores in China currently for sale | $ / shares	$ 0.04				$ 0.02