Leases (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 23, 2020 USD ($) restaurant lease	Sep. 25, 2019 USD ($) restaurant	Sep. 23, 2020 USD ($) lease restaurant	Sep. 25, 2019 USD ($) restaurant	Dec. 25, 2019 USD ($)	Dec. 27, 2018 USD ($)
Lessee, Lease, Description [Line Items]
Operating Lease, Payments			$ 17,276	$ 19,789
Property and equipment held under operating leases, net ("ROU asset")	$ 180,781		180,781		$ 192,395	$ 205,200
Finance Lease, Right-of-Use Asset, Amortization				9
Finance Lease, Interest Expense	5	$ 9	16	24
Operating Lease, Cost	6,799	6,847	20,488	20,688
Short-term Lease, Cost	6	9	18	26
Variable Lease, Cost	166	159	445	482
Sublease Income	(883)	(722)	(2,424)	(1,623)
Total lease cost	6,093	$ 6,302	18,543	19,606
Operating Lease, Liability	$ 202,600		202,600		$ 213,898	$ 222,300
Finance Lease, Principal Payments			26	61
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability			3,221	$ 8,868
Derecognition of ROU assets due to terminations, impairment or modifications			$ (569)
Number of Restaurants with lease modification | restaurant	2	3	9	6
Operating Lease, Lease Income	$ 100	$ 100	$ 400	$ 400
Impairment of Right-of-Use Assets			$ 543
Initial lease term	20 years		20 years
Operating Lease, Impairment Loss		0	$ 500	0
Depreciation and amortization [Member]
Lessee, Lease, Description [Line Items]
Total lease cost	$ 5		16	9
Operating Expense [Member]
Lessee, Lease, Description [Line Items]
Total lease cost	5,786	6,015	17,582	18,675
General and Administrative Expense
Lessee, Lease, Description [Line Items]
Total lease cost	114	116	344	348
Interest Expense
Lessee, Lease, Description [Line Items]
Total lease cost		9		24
Restructuring Charges [Member]
Lessee, Lease, Description [Line Items]
Total lease cost	$ 188	$ 162	$ 601	$ 550
Minimum
Lessee, Lease, Description [Line Items]
Lessor, Operating Lease, Term of Contract	3 years		3 years
Renewal term	4 years		4 years
Maximum
Lessee, Lease, Description [Line Items]
Lessor, Operating Lease, Term of Contract	20 years		20 years
Renewal term	5 years		5 years
Texas
Lessee, Lease, Description [Line Items]
Number Of Restaurant Closed | restaurant		1		1
Number of restaurants primarily responsible for impairment | restaurant			1
Property lease modification [Member]
Lessee, Lease, Description [Line Items]
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 300	$ 2,000	$ 2,000	$ 3,300
Property Lease [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Payments			16,348	18,819
Finance Lease, Right-of-Use Asset, Amortization				9
Finance Lease, Interest Expense	5	9	16	24
Operating Lease, Cost	6,502	6,534	19,577	19,721
Variable Lease, Cost	116	121	325	346
Sublease Income	(883)	(722)	(2,424)	(1,623)
Total lease cost	$ 5,740	$ 5,942	17,494	18,477
Finance Lease, Principal Payments			24	61
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability			3,180	$ 8,832
Derecognition of ROU assets due to terminations, impairment or modifications			$ (543)
Finance Lease, Weighted Average Remaining Lease Term	2 years 29 days	3 years 29 days	2 years 29 days	3 years 29 days
Operating Lease, Weighted Average Discount Rate, Percent	4.31%	4.40%	4.31%	4.40%
Operating Lease, Weighted Average Remaining Lease Term	11 years 7 months 13 days	12 years 2 months 15 days	11 years 7 months 13 days	12 years 2 months 15 days
Finance Lease, Weighted Average Discount Rate, Percent	11.10%	11.10%	11.10%	11.10%
Facility Leases [Member]
Lessee, Lease, Description [Line Items]
Number Of Finance Leases | lease	1		1
Equipment Lease [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Payments			$ 928	$ 970
Operating Lease, Cost	$ 297	$ 313	911	967
Short-term Lease, Cost	6	9	18	26
Variable Lease, Cost	50	38	120	136
Total lease cost	$ 353	$ 360	1,049	1,129
Finance Lease, Principal Payments			2
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability			41	$ 36
Derecognition of ROU assets due to terminations, impairment or modifications			$ (26)
Finance Lease, Weighted Average Remaining Lease Term	4 years 9 months 29 days	0 years	4 years 9 months 29 days	0 years
Operating Lease, Weighted Average Discount Rate, Percent	3.89%	4.00%	3.89%	4.00%
Operating Lease, Weighted Average Remaining Lease Term	2 years 7 months 2 days	3 years 29 days	2 years 7 months 2 days	3 years 29 days
Finance Lease, Weighted Average Discount Rate, Percent	1.68%		1.68%
Number Of Finance Leases | lease	2		2
Lease Not Yet Commenced [Member]
Lessee, Lease, Description [Line Items]
Number Of Leases | lease			3