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 (Loss)	Non- Controlling Interest
Beginning balance (shares) at Dec. 27, 2017		26,527,477	10,250,007	26,527,477	10,250,007
Beginning balance at Dec. 27, 2017	$ 224,479			$ 27	$ 10	$ 153,105	$ 16,399	$ (49)	$ 54,987
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	15,550						11,112		4,438
Other comprehensive income:
Net change related to available-for-sale securities	13							10	3
Equity-based compensation	2,873					2,873
Activity under stock compensation plans (in shares)				253,439
Activity under stock compensation plans	3,566					2,103			1,463
Redemption of LLC Interests (in shares)				1,325,415	1,325,415
Redemption of LLC Interests	0			$ 1	$ (1)	7,359			(7,359)
Establishment of liabilities under tax receivable agreement and related changes to deferred tax assets associated with increases in tax basis	12,210					12,210
Distributions paid to non-controlling interest holders	(670)								(670)
Ending balance (shares) at Jun. 27, 2018		28,106,331	8,924,592	28,106,331	8,924,592
Ending balance at Jun. 27, 2018	256,447			$ 28	$ 9	177,650	26,337	0	52,423
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of accounting changes | Adjustments for New Accounting Pronouncement	(1,574)						(1,174)	39	(439)
Net income	10,571
Other comprehensive income:
Net change related to available-for-sale securities	0							0
Ending balance (shares) at Jun. 27, 2018		28,106,331	8,924,592	28,106,331	8,924,592
Ending balance at Jun. 27, 2018	$ 256,447			$ 28	$ 9	$ 177,650	$ 26,337	$ 0	$ 52,423