Selected Quarterly Financial and Earnings Data (Unaudited) Quarterly Table (Details) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Jan. 01, 2017 USD ($) $ / shares	Oct. 02, 2016 USD ($) $ / shares	Jul. 03, 2016 USD ($) $ / shares	Apr. 03, 2016 USD ($) $ / shares	Jan. 03, 2016 USD ($) $ / shares	Sep. 27, 2015 USD ($) $ / shares	Jun. 28, 2015 USD ($) $ / shares	Mar. 29, 2015 USD ($) $ / shares	Jan. 01, 2017 USD ($) $ / shares	Jan. 03, 2016 USD ($) $ / shares	Dec. 28, 2014 USD ($) $ / shares
Quarterly Financial Information Disclosure [Abstract]
Restaurant sales	$ 240,826	$ 238,870	$ 241,368	$ 222,519	$ 229,056	$ 217,676	$ 219,102	$ 193,170	$ 943,583	$ 859,004	$ 692,755
Operating income (loss)	6,077	9,049	13,896	6,680	11,561	11,751	12,358	(4,462)	35,702	31,208	(7,551)
Net income (loss)	$ 29,462	$ 4,489	$ 9,376	$ 2,145	$ 7,018	$ 7,239	$ (4,977)	$ (9,276)	$ 45,472	$ 4	$ (38,117)
Basic and diluted net income (loss) per share | $ / shares	$ 0.65	$ 0.10	$ 0.21	$ 0.05	$ 0.16	$ 0.16	$ (0.14)	$ (0.27)	$ 1.01	$ 0.00	$ (1.23)
Restaurants at end of period	753	734	723	717	705	660	657	659	753	705