Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended
	Mar. 30, 2021	Mar. 31, 2020
Revenue:
Total revenue	$ 109,577	$ 100,348
Restaurant operating costs (exclusive of depreciation and amortization shown separately below):
Other restaurant operating costs	20,205	16,689
General and administrative	10,929	10,554
Depreciation and amortization	5,587	5,335
Pre-opening	58	73
Restaurant impairments, closure costs and asset disposals	1,231	1,056
Total costs and expenses	110,942	105,202
Loss from operations	(1,365)	(4,854)
Interest expense, net	622	968
Loss before taxes	(1,987)	(5,822)
(Benefit) provision for income taxes	(10)	13
Net loss	$ (1,977)	$ (5,835)
Earnings Per Share [Abstract]
Basic (USD per share)	$ (0.04)	$ (0.13)
Diluted (USD per share)	$ (0.04)	$ (0.13)
Weighted average shares of Class A and Class B common stock outstanding, combined:
Basic (in shares)	45,098,028	44,142,220
Diluted (in shares)	45,098,028	44,142,220
Restaurant revenue
Revenue:
Total revenue	$ 107,744	$ 98,716
Restaurant operating costs (exclusive of depreciation and amortization shown separately below):
Restaurant operating costs	26,977	25,204
Franchising royalties and fees, and other
Revenue:
Total revenue	1,833	1,632
Labor
Restaurant operating costs (exclusive of depreciation and amortization shown separately below):
Restaurant operating costs	34,306	34,231
Occupancy
Restaurant operating costs (exclusive of depreciation and amortization shown separately below):
Restaurant operating costs	$ 11,649	$ 12,060