Condensed Consolidated Statements of Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 28, 2017	Jun. 29, 2016	Jun. 28, 2017	Jun. 29, 2016
Income Statement [Abstract]
Company Restaurant Expenses	$ 77,312	$ 70,889	$ 151,759	$ 140,998
Revenue
Company-operated restaurant revenue	98,885	90,877	192,334	179,246
Franchise revenue	6,688	6,597	13,010	12,582
Total revenue	105,573	97,474	205,344	191,828
Cost of operations
Food and paper cost	29,146	27,032	56,218	53,800
Labor and related expenses	26,592	24,361	53,425	48,868
Occupancy and other operating expenses	21,574	19,496	42,116	38,330
General and administrative expenses	9,576	8,287	19,309	17,524
Franchise expenses	1,006	1,239	1,823	2,163
Depreciation and amortization	4,632	3,964	8,949	7,722
Loss on disposal of assets	434	267	659	466
Expenses related to fire loss	0	0	0	48
Gain on recovery of insurance proceeds, property, equipment and expenses	0		0	(889)
Gain On Business Interruption Insurance Recovery Property Equipment And Expenses		(600)		(889)
Recovery of securities class action legal expense	(511)	0	(511)	0
Asset impairment and closed-store reserves	384	60	1,255	134
Costs and Expenses	92,833	84,106	183,243	168,166
Gain (Loss) on Disposition of Business	0	33	0	33
Income from operations	12,740	13,401	22,101	23,695
Interest expense-net of interest income of $6 and $7 for the quarters ended June 28, 2017 and June 29, 2016, respectively and $11 and $15 for year-to-date ended June 28, 2017 and June 29, 2016, respectively.	778	830	1,568	1,656
Income tax receivable agreement (income) expense	(101)	(35)	126	229
Income before provision for income taxes	12,063	12,606	20,407	21,810
Provision for income taxes	4,244	5,339	7,711	9,100
Net income	$ 7,819	$ 7,267	$ 12,696	$ 12,710
Net income per share
Basic (usd per share)	$ 0.20	$ 0.19	$ 0.33	$ 0.33
Diluted (usd per share)	$ 0.20	$ 0.19	$ 0.32	$ 0.33
Weighted-average shares used in computing net income per share
Basic (shares)	38,449,240	38,294,575	38,443,130	38,289,505
Diluted (shares)	39,123,961	38,962,802	39,102,501	38,981,610