Quarterly Financial Information - Schedule of Quarterly Financial Information (Detail) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 28, 2016 USD ($) Restaurants $ / shares $ / Restaurant shares	Sep. 28, 2016 USD ($) Restaurants $ / shares $ / Restaurant shares	Jun. 29, 2016 USD ($) Restaurants $ / shares $ / Restaurant shares	Mar. 30, 2016 USD ($) Restaurants $ / shares $ / Restaurant shares	Dec. 30, 2015 USD ($) Restaurants $ / shares $ / Restaurant shares	Sep. 30, 2015 USD ($) Restaurants $ / shares $ / Restaurant shares	Jul. 01, 2015 USD ($) Restaurants $ / shares $ / Restaurant shares	Apr. 01, 2015 USD ($) Restaurants $ / shares $ / Restaurant shares	Dec. 28, 2016 USD ($) Restaurants $ / shares shares	Dec. 30, 2015 USD ($) Restaurants $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Sep. 24, 2014 Restaurants
Selected Financial Data
Total revenue | $	$ 92,479	$ 95,816	$ 97,474	$ 94,354	$ 86,307	$ 88,870	$ 89,454	$ 90,426	$ 380,123	$ 355,057	$ 344,861
Income from Operations | $	1,926	9,008	13,401	10,294	9,748	12,527	13,582	12,967	34,629	48,824	49,284
Provision for income taxes | $	853	2,830	5,339	3,761	4,576	6,505	5,062	4,714	12,783	20,857	(63,008)
Net income | $	$ 418	$ 5,211	$ 7,267	$ 5,443	$ 5,367	$ 4,666	$ 7,230	$ 6,791	$ 18,339	$ 24,054	$ 42,463
Net income per share:
Basic | $ / shares	$ 0.01	$ 0.14	$ 0.19	$ 0.14	$ 0.14	$ 0.12	$ 0.19	$ 0.18	$ 0.48	$ 0.63	$ 1.32
Diluted | $ / shares	$ 0.01	$ 0.13	$ 0.19	$ 0.14	$ 0.14	$ 0.12	$ 0.18	$ 0.17	$ 0.47	$ 0.62	$ 1.24
Weighted average shares used in computing net income per share:
Basic | shares	38,437,020	38,415,189	38,294,575	38,284,435	38,284,435	38,275,317	37,812,767	37,424,745	38,357,805	37,949,316	32,285,484
Diluted | shares	39,108,967	39,083,577	38,962,802	39,001,078	38,965,248	39,107,241	39,085,206	38,921,884	39,026,950	39,039,558	34,346,241
Selected Operating Data
Company-operated | Restaurants												6
Average unit volume (AUV) (company-operated) | $ / Restaurant	1,790	1,929	1,970	1,936	1,826	1,928	1,952	1,963
Comparable restaurant sales growth
Restaurant contribution margin	18.50%	20.90%	22.00%	20.70%	21.50%	21.20%	21.60%	23.30%
Entity Operated Units [Member]
Selected Operating Data
Company-operated | Restaurants	201	193	188	188	186	175	174	173	201	186
Comparable restaurant sales growth
Company-operated	(0.60%)	1.40%	2.00%	(0.60%)	1.00%	0.00%	(0.50%)	3.50%
Franchised Units [Member]
Selected Operating Data
Company-operated | Restaurants	259	253	251	248	247	245	244	243	259	247
Comparable restaurant sales growth
Company-operated	(1.90%)	1.80%	2.70%	1.80%	2.40%	1.10%	2.60%	6.20%
System Wide [Member]
Selected Operating Data
Company-operated | Restaurants	460	446	439	436	433	420	418	416	460	433
Comparable restaurant sales growth
Company-operated	(1.30%)	1.60%	2.40%	0.70%	1.80%	0.60%	1.30%	5.10%