Impairment Of Long-Lived Assets And Other Lease Charges (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Apr. 01, 2018 USD ($)	Apr. 02, 2017 USD ($)	Dec. 31, 2017 USD ($)
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment and other lease charges	$ 309	$ 531
Asset impairment charges	100	$ 400
Sale leaseback transaction loss	100
Asset impairment charges, number of restaurants		3
Other lease charges	$ (4)		$ 81
Other lease charges, number of restaurants	2	3
Provisions for restaurant closures	$ 87		$ 1,174
Restructuring, settlement and impairment provisions		$ 500
Previously Impaired [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment charges	100	200
Closed Restaurants [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Other lease charges	$ 100	$ 100