Selected Quarterly Financial and Earnings Data (Unaudited) Quarterly Table (Details) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Jan. 02, 2022 USD ($) $ / shares	Oct. 03, 2021 USD ($) $ / shares	Jul. 04, 2021 USD ($) $ / shares	Apr. 04, 2021 USD ($) $ / shares	Jan. 03, 2021 USD ($) $ / shares	Sep. 27, 2020 USD ($) $ / shares	Jun. 28, 2020 USD ($) $ / shares	Mar. 29, 2020 USD ($) $ / shares	Jan. 02, 2022 USD ($) $ / shares	Jan. 03, 2021 USD ($) $ / shares	Dec. 29, 2019 USD ($) $ / shares
Quarterly Financial Information Disclosure [Abstract]
Restaurant sales	$ 416,133	$ 421,703	$ 424,541	$ 389,993	$ 420,530	$ 407,036	$ 368,418	$ 351,518
Operating income (loss)	(9,998)	(3,647)	5,889	(3,103)	1,631	10,228	14,302	(22,047)	$ (10,859)	$ 4,114	$ (8,743)
Net income (loss)	$ (16,400)	$ (9,902)	$ (9,559)	$ (7,168)	$ (18,627)	$ 3,531	$ 7,842	$ (22,209)	$ (43,029)	$ (29,463)	$ (31,919)
Basic and diluted net income (loss) per share | $ / shares	$ (0.33)	$ (0.20)	$ (0.19)	$ (0.14)	$ (0.37)	$ 0.06	$ 0.13	$ (0.44)	$ (0.86)	$ (0.58)	$ (0.74)
Restaurants at end of period	1,091	1,092	1,092	1,075	1,074	1,088	1,092	1,093	1,091	1,074