Selected Quarterly Financial and Earnings Data (Unaudited) Quarterly Table (Details) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 29, 2019 USD ($) $ / shares	Sep. 29, 2019 USD ($) $ / shares	Jun. 30, 2019 USD ($) $ / shares	Mar. 31, 2019 USD ($) $ / shares	Dec. 30, 2018 USD ($) $ / shares	Sep. 30, 2018 USD ($) $ / shares	Jul. 01, 2018 USD ($) $ / shares	Apr. 01, 2018 USD ($) $ / shares	Dec. 29, 2019 USD ($) $ / shares	Dec. 30, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($) $ / shares
Quarterly Financial Information Disclosure [Abstract]
Restaurant sales	$ 397,639	$ 398,414	$ 365,674	$ 290,789	$ 307,754	$ 296,917	$ 303,050	$ 271,586
Operating income (loss)	(4,563)	(1,115)	2,103	(5,168)	7,190	9,668	13,833	2,664	$ (8,743)	$ 33,355	$ 29,473
Net income (loss)	$ (9,906)	$ (6,812)	$ (3,732)	$ (11,469)	$ 1,807	$ 3,611	$ 7,788	$ (3,102)	$ (31,919)	$ 10,104	$ 7,159
Basic and diluted net income (loss) per share | $ / shares	$ (0.20)	$ (0.15)	$ (0.09)	$ (0.32)	$ 0.04	$ 0.08	$ 0.17	$ (0.09)	$ (0.74)	$ 0.22	$ 0.16
Restaurants at end of period	1,101	1,088	1,081	845	849	838	807	807	1,101	849