CONDENSED CONSOLIDATED STATEMENT OF STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	Class A Common Stock	Class B Common Stock	Common Stock [Member] Class A Common Stock	Common Stock [Member] Class B Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income	Non- Controlling Interest
Beginning balance (shares) at Dec. 26, 2018				29,520,833	7,557,347
Beginning balance at Dec. 26, 2018	$ 273,455			$ 30	$ 8	$ 195,633	$ 30,404	$ 0	$ 47,380
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	14,778						11,576		3,202
Other comprehensive income:
Net change in foreign currency translation adjustment	0
Equity-based compensation	4,010					4,010
Activity under stock compensation plans (in shares)				210,714
Activity under stock compensation plans	2,091			$ 0		932			1,159
Redemption of LLC Interests (in shares)				826,138	(826,138)
Redemption of LLC Interests	0			$ 1	$ (1)	5,480			(5,480)
Establishment of liabilities under tax receivable agreement and related changes to deferred tax assets associated with increases in tax basis	2,811					2,811
Distributions paid to non-controlling interest holders	(1,667)								(1,667)
Ending balance (shares) at Jun. 26, 2019				30,557,685	6,731,209
Ending balance at Jun. 26, 2019	300,673			$ 31	$ 7	208,866	46,116	0	45,653
Beginning balance (shares) at Mar. 27, 2019				29,698,228	7,453,515
Beginning balance at Mar. 27, 2019	285,738			$ 31	$ 7	199,315	37,086	0	49,299
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	11,171						9,030		2,141
Other comprehensive income:
Net change in foreign currency translation adjustment	0
Equity-based compensation	2,263					2,263
Activity under stock compensation plans (in shares)				137,151
Activity under stock compensation plans	614					(43)			657
Redemption of LLC Interests (in shares)				722,306	(722,306)
Redemption of LLC Interests	0					4,886			(4,886)
Establishment of liabilities under tax receivable agreement and related changes to deferred tax assets associated with increases in tax basis	2,445					2,445
Distributions paid to non-controlling interest holders	(1,558)								(1,558)
Ending balance (shares) at Jun. 26, 2019				30,557,685	6,731,209
Ending balance at Jun. 26, 2019	300,673			$ 31	$ 7	208,866	46,116	0	45,653
Beginning balance (shares) at Dec. 25, 2019		34,417,302	3,145,197	34,417,302	3,145,197
Beginning balance at Dec. 25, 2019	321,985			$ 35	$ 3	244,410	54,367	2	23,168
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(19,110)						(17,171)		(1,939)
Other comprehensive income:
Net change in foreign currency translation adjustment	1							1
Equity-based compensation	2,742					2,742
Activity under stock compensation plans (in shares)				141,504
Activity under stock compensation plans	(29)			$ 0		260			(289)
Redemption of LLC Interests (in shares)				28,195	(28,195)
Redemption of LLC Interests	0			$ 0		195			(195)
Establishment of liabilities under tax receivable agreement and related changes to deferred tax assets associated with increases in tax basis	1,013					1,013
Issuance of Class A common stock sold in equity offerings, net of underwriting discounts, commissions and offering costs (in shares)				3,649,537
Issuance of Class A common stock sold in equity offerings, net of underwriting discounts, commissions and offering costs	144,997			$ 3		135,718			9,276
Distributions paid to non-controlling interest holders	(314)								(314)
Ending balance (shares) at Jun. 24, 2020		38,236,538	3,117,002	38,236,538	3,117,002
Ending balance at Jun. 24, 2020	451,285			$ 38	$ 3	384,338	37,196	3	29,707
Beginning balance (shares) at Mar. 25, 2020				34,523,400	3,117,002
Beginning balance at Mar. 25, 2020	322,606			$ 35	$ 3	246,970	53,407	3	22,188
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(18,031)						(16,211)		(1,820)
Other comprehensive income:
Net change in foreign currency translation adjustment	0
Equity-based compensation	1,429					1,429
Activity under stock compensation plans (in shares)				63,601
Activity under stock compensation plans	(92)					(164)			72
Redemption of LLC Interests (in shares)				0
Redemption of LLC Interests	0
Establishment of liabilities under tax receivable agreement and related changes to deferred tax assets associated with increases in tax basis	385					385
Issuance of Class A common stock sold in equity offerings, net of underwriting discounts, commissions and offering costs (in shares)				3,649,537
Issuance of Class A common stock sold in equity offerings, net of underwriting discounts, commissions and offering costs	144,997			$ 3		135,718			9,276
Distributions paid to non-controlling interest holders	(9)								(9)
Ending balance (shares) at Jun. 24, 2020		38,236,538	3,117,002	38,236,538	3,117,002
Ending balance at Jun. 24, 2020	$ 451,285			$ 38	$ 3	$ 384,338	$ 37,196	$ 3	$ 29,707