Selected Quarterly Financial Data (unaudited) (Details) $ / shares in Units, $ in Thousands	3 Months Ended									12 Months Ended
	Dec. 31, 2019 USD ($) restaurant $ / shares	Oct. 01, 2019 USD ($) restaurant $ / shares	Jul. 02, 2019 USD ($) $ / shares	Apr. 02, 2019 USD ($) $ / shares	Jan. 01, 2019 USD ($) restaurant $ / shares	Oct. 02, 2018 USD ($) restaurant $ / shares	Jul. 03, 2018 USD ($) restaurant $ / shares	Apr. 03, 2018 USD ($) restaurant $ / shares	Apr. 04, 2017 restaurant	Dec. 31, 2019 USD ($) restaurant $ / shares	Jan. 01, 2019 USD ($) restaurant $ / shares	Jan. 02, 2018 USD ($) restaurant $ / shares
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 113,871	$ 118,304	$ 120,190	$ 110,046	$ 113,193	$ 116,727	$ 117,395	$ 110,526		$ 462,411	$ 457,841	$ 456,492
Income (loss) from operations	247	5,044	1,238	(1,090)	950	2,132	(4,162)	(2,678)		5,439	(3,758)	(33,850)
Net income (loss)	$ (1,183)	$ 4,243	$ 438	$ (1,851)	$ 19	$ 1,050	$ (5,935)	$ (3,575)		$ 1,647	$ (8,441)	$ (37,482)
Basic EPS (USD per share) | $ / shares	$ (0.03)	$ 0.10	$ 0.10	$ (0.04)	$ 0	$ 0.02	$ (0.14)	$ (0.09)		$ 0.04	$ (0.20)	$ (1.20)
Diluted EPS (USD per share) | $ / shares	$ (0.03)	$ 0.09	$ 0.10	$ (0.04)	$ 0	$ 0.02	$ (0.14)	$ (0.09)		$ 0.04	$ (0.20)	$ (1.20)
Impairment of restaurants			$ 2,200					$ 400
Number of restaurants impaired | restaurant	0	0			0	0	0			2	1	34
Write down related to assets held for sale	$ 3,600
Data breach liabilities							$ 3,400
Gift card liability	$ 2,398				$ 3,284		$ 300			$ 2,398	$ 3,284
Number of restaurants closed | restaurant					7	3	7	2	55	5	19
Closure costs					$ 600	$ 1,500	$ 1,500	$ 600