Quarterly Results of Operations (Unaudited) - Schedule of Quarterly Financial Information (Detail) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	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. 28, 2016 USD ($) restaurant $ / shares $ / restaurant shares	Sep. 28, 2016 USD ($) restaurant $ / shares $ / restaurant shares	Jun. 29, 2016 USD ($) restaurant $ / shares $ / restaurant shares	Mar. 30, 2016 USD ($) restaurant $ / shares $ / restaurant shares	Dec. 27, 2017 USD ($) restaurant $ / shares shares	Dec. 28, 2016 USD ($) restaurant $ / shares shares	Dec. 30, 2015 USD ($) $ / shares shares
Selected Financial Data
Total revenue	$ 95,202	$ 101,155	$ 105,573	$ 99,771	$ 92,479	$ 95,816	$ 97,474	$ 94,354	$ 401,701	$ 380,123	$ 355,057
(Loss) income from Operations	(9,665)	(5,612)	12,740	9,361	1,926	9,008	13,401	10,294	6,824	34,629	48,824
(Benefit) provision for income taxes	(4,757)	(2,457)	4,244	3,467	853	2,830	5,339	3,761	497	12,783	20,857
Net income (loss)	$ (38)	$ (4,039)	$ 7,819	$ 4,877	$ 418	$ 5,211	$ 7,267	$ 5,443	$ 8,619	$ 18,339	$ 24,054
Net income (loss) per share:
Basic (usd per share) | $ / shares	$ 0.00	$ (0.11)	$ 0.20	$ 0.13	$ 0.01	$ 0.14	$ 0.19	$ 0.14	$ 0.22	$ 0.48	$ 0.63
Diluted (usd per share) | $ / shares	$ 0.00	$ (0.11)	$ 0.20	$ 0.12	$ 0.01	$ 0.13	$ 0.19	$ 0.14	$ 0.22	$ 0.47	$ 0.62
Weighted average shares used in computing net income per share:
Basic (shares) | shares	38,465,208	38,462,100	38,449,240	38,437,020	38,437,020	38,415,189	38,294,575	38,284,435	38,453,347	38,357,805	37,949,316
Diluted (shares) | shares	38,465,208	38,462,100	39,123,961	39,079,007	39,108,967	39,083,577	38,962,802	39,001,078	39,086,676	39,026,950	39,039,558
Selected Operating Data
Average unit volume (AUV) (usd per restaurant) | $ / restaurant	1,787	1,922	1,995	1,913	1,790	1,929	1,970	1,936
Comparable restaurant sales growth
Restaurant contribution margin (%)	18.40%	18.30%	21.80%	20.30%	18.50%	20.90%	22.00%	20.70%
Tax Cuts and Jobs Act of 2017, decrease in deferred tax liability	$ 1,400
TRA tax benefit									$ 2,000
Anti-dilutive securities not considered in diluted EPS calculation (shares) | shares	0	0							747,985	468,705	214,411
Company-operated
Selected Operating Data
Number of restaurants (at period end) | restaurant	212	208	208	204	201	193	188	188	212	201
Comparable restaurant sales growth
Comparable restaurant sales growth (%)	0.90%	0.90%	2.40%	(0.40%)	(0.60%)	1.40%	2.00%	(0.60%)
Franchised
Selected Operating Data
Number of restaurants (at period end) | restaurant	265	265	264	263	259	253	251	248	265	259
Comparable restaurant sales growth
Comparable restaurant sales growth (%)	1.90%	2.40%	3.20%	(0.20%)	(1.90%)	1.80%	2.70%	1.80%
System-wide
Selected Operating Data
Number of restaurants (at period end) | restaurant	477	473	472	467	460	446	439	436	477	460
Comparable restaurant sales growth
Comparable restaurant sales growth (%)	1.40%	1.70%	2.90%	(0.30%)	(1.30%)	1.60%	2.40%	0.70%