Quarterly Results of Operations (Unaudited) - Schedule of Quarterly Financial Information (Details) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 26, 2018 USD ($) restaurant $ / shares $ / restaurant shares	Sep. 26, 2018 USD ($) restaurant $ / shares $ / restaurant shares	Jun. 27, 2018 USD ($) restaurant $ / shares $ / restaurant shares	Mar. 28, 2018 USD ($) restaurant $ / shares $ / restaurant shares	Dec. 27, 2017 USD ($) restaurant $ / shares $ / restaurant shares	Sep. 27, 2017 USD ($) restaurant $ / shares $ / restaurant shares	Jun. 28, 2017 USD ($) restaurant $ / shares $ / restaurant shares	Mar. 29, 2017 USD ($) restaurant $ / shares $ / restaurant shares	Dec. 26, 2018 USD ($) restaurant $ / shares shares	Dec. 27, 2017 USD ($) restaurant $ / shares shares	Dec. 28, 2016 USD ($) restaurant $ / shares shares
Selected Financial Data
Total revenue | $	$ 106,261	$ 112,178	$ 111,633	$ 105,756	$ 95,202	$ 101,155	$ 105,573	$ 99,771	$ 435,828	$ 401,701	$ 380,123
(Loss) income from operations | $	(30,990)	9,492	7,589	4,448	(9,665)	(5,612)	12,740	9,361	(9,461)	6,824	34,629
Provision (benefit) for income taxes ($) | $	(8,410)	2,388	865	1,949	(4,757)	(2,457)	4,244	3,467	(3,208)	497	12,783
Net (loss) income | $	$ (23,410)	$ 6,835	$ 5,052	$ 2,529	$ (38)	$ (4,039)	$ 7,819	$ 4,877	$ (8,994)	$ 8,619	$ 18,339
Net (loss) income per share:
Basic (usd per share) | $ / shares	$ (0.60)	$ 0.18	$ 0.13	$ 0.07	$ 0.00	$ (0.11)	$ 0.20	$ 0.13	$ (0.23)	$ 0.22	$ 0.48
Diluted (usd per share) | $ / shares	$ (0.60)	$ 0.17	$ 0.13	$ 0.06	$ 0.00	$ (0.11)	$ 0.20	$ 0.12	$ (0.23)	$ 0.22	$ 0.47
Weighted average shares used in computing net (loss) income per share:
Basic (shares) | shares	38,751,522	38,602,658	38,482,074	38,465,208	38,465,208	38,462,100	38,449,240	38,437,020	38,574,553	38,453,347	38,357,805
Diluted (shares) | shares	38,751,522	39,205,090	39,043,434	38,987,351	38,465,208	38,462,100	39,123,961	39,079,007	38,574,553	39,086,676	39,026,950
Selected Operating Data
Number of restaurants (at period end) | restaurant	4				23				4	23	9
Average unit volume (AUV) (usd per restaurant) | $ / restaurant	1,785	1,891	1,890	1,791	1,787	1,922	1,995	1,913
Company-operated
Selected Operating Data
Number of restaurants (at period end) | restaurant	213	212	211	212	212	208	208	204	213	212
Comparable restaurant sales growth (%)
Comparable restaurant sales growth (%)	3.70%	2.00%	(1.60%)	(2.00%)	0.90%	0.90%	2.40%	(0.40%)
Franchised
Selected Operating Data
Number of restaurants (at period end) | restaurant	271	271	269	268	265	265	264	263	271	265
Comparable restaurant sales growth (%)
Comparable restaurant sales growth (%)	5.10%	3.00%	(0.30%)	(0.40%)	1.90%	2.40%	3.20%	(0.20%)
System-wide
Selected Operating Data
Number of restaurants (at period end) | restaurant	484	483	480	480	477	473	472	467	484	477
Comparable restaurant sales growth (%)
Comparable restaurant sales growth (%)	4.40%	2.60%	(0.90%)	(1.10%)	1.40%	1.70%	2.90%	(0.30%)