Selected Quarterly Financial Data (Details) $ / shares in Units, $ in Thousands	3 Months Ended									12 Months Ended
	Jan. 01, 2019 USD ($) restaurant $ / shares	Oct. 02, 2018 USD ($) restaurant $ / shares	Jul. 03, 2018 USD ($) restaurant $ / shares	Apr. 03, 2018 USD ($) restaurant $ / shares	Jan. 02, 2018 USD ($) restaurant $ / shares	Oct. 03, 2017 USD ($) restaurant $ / shares	Jul. 04, 2017 USD ($) restaurant $ / shares	Apr. 04, 2017 USD ($) restaurant $ / shares	Dec. 29, 2015 restaurant	Jan. 01, 2019 USD ($) restaurant $ / shares	Jan. 02, 2018 USD ($) restaurant $ / shares	Jan. 03, 2017 USD ($) restaurant $ / shares
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 113,193	$ 116,727	$ 117,395	$ 110,526	$ 112,774	$ 114,211	$ 112,792	$ 116,715		$ 457,841	$ 456,492	$ 487,474
Operating income	950	2,132	(4,162)	(2,678)	87	(7,483)	(808)	(25,646)		(3,758)	(33,850)	(67,528)
Net loss	$ 19	$ 1,050	$ (5,935)	$ (3,575)	(487)	(8,335)	(1,815)	(26,845)		(8,441)	(37,482)	(71,677)
Net loss attributable to common stockholders					$ (487)	$ (8,335)	$ (8,816)	$ (27,810)		$ (8,441)	$ (45,449)	$ (71,677)
Basic EPS (USD per share) | $ / shares	$ 0	$ 0.02	$ (0.14)	$ (0.09)	$ (0.01)	$ (0.20)	$ (0.22)	$ (0.99)		$ (0.20)	$ (1.20)	$ (2.58)
Diluted EPS (USD per share) | $ / shares	$ 0	$ 0.02	$ (0.14)	$ (0.09)	$ (0.01)	$ (0.20)	$ (0.22)	$ (0.99)		$ (0.20)	$ (1.20)	$ (2.58)
Closure costs								$ 19,900		$ 4,149	$ 20,052	$ 2,251
Impairment costs related to closure of restaurants						$ 9,100
Number of restaurants closed | restaurant	7	3	7	2				55	16	19
Closure costs	$ 600	$ 1,500	$ 1,500	$ 600
Number of restaurants impaired | restaurant	0	0	0	1	3	18	9	4		1	34	54
Impairment costs of restaurants				$ 400	$ 1,100		$ 4,000	$ 1,900
Data breach liabilities	$ 0		$ 3,400		7,605					$ 0	$ 7,605
Gift card liability	$ 3,284		$ 300		$ 4,078					$ 3,284	$ 4,078