Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2020	Oct. 01, 2019	Sep. 29, 2020	Oct. 01, 2019
Revenue:
Total revenue	$ 105,982	$ 118,304	$ 286,487	$ 348,540
Restaurant operating costs (exclusive of depreciation and amortization shown):
Other restaurant operating costs	19,383	17,161	51,861	50,475
General and administrative	10,827	10,436	31,415	32,424
Depreciation and amortization	5,541	5,458	16,273	16,626
Pre-opening	239	266	383	331
Restaurant impairments, closure costs and asset disposals	369	336	3,983	3,640
Total costs and expenses	105,260	113,260	303,144	343,348
Income (loss) from operations	722	5,044	(16,657)	5,192
Interest expense, net	822	737	2,710	2,298
(Loss) income before taxes	(100)	4,307	(19,367)	2,894
Provision for income taxes	27	64	73	64
Net (loss) income and comprehensive (loss) income	$ (127)	$ 4,243	$ (19,440)	$ 2,830
Earnings Per Share [Abstract]
Basic (USD per share)	$ 0	$ 0.10	$ (0.44)	$ 0.06
Diluted (USD per share)	$ 0	$ 0.09	$ (0.44)	$ 0.06
Weighted average shares of Class A and Class B common stock outstanding, combined:
Basic (in shares)	44,358,763	43,990,049	44,238,400	44,007,345
Diluted (in shares)	44,358,763	44,899,176	44,238,400	45,078,539
Restaurant revenue
Revenue:
Total revenue	$ 104,413	$ 116,759	$ 283,150	$ 344,382
Restaurant operating costs (exclusive of depreciation and amortization shown):
Restaurant operating costs	25,900	29,544	71,124	89,083
Franchising royalties and fees, and other
Revenue:
Total revenue	1,569	1,545	3,337	4,158
Labor
Restaurant operating costs (exclusive of depreciation and amortization shown):
Restaurant operating costs	31,264	37,951	92,632	113,920
Occupancy
Restaurant operating costs (exclusive of depreciation and amortization shown):
Restaurant operating costs	$ 11,737	$ 12,108	$ 35,473	$ 36,849