Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock Common Class A	Common Stock Common Class B	Additional Paid-in Capital	Accumulated Other Comprehensive (Loss) Income, net of tax	Retained Earnings
Balance at Dec. 30, 2017	$ 423,523	$ 86	$ 30	$ 372,590	$ (1,288)	$ 52,105
Balance (in shares) at Dec. 30, 2017		8,603,000	3,018,000
Net income	9,310					9,310
Stock options exercised and restricted shares activities (in shares)		188,000
Stock options exercised and restricted shares activities	20,234	$ 2		20,232
Stock-based compensation expense	1,491			1,491
Repurchase of Class A Common Stock (in shares)		(91,000)
Repurchase of Class A Common Stock	(16,639)	$ (1)				(16,638)
Currency translation adjustment	(11)				(11)
One time effect of adoption of ASU 2014-09,Revenue from Contracts with Customers, net of tax of $329	1,000					(982)
One time effect of adoption of ASU 2018-02, Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income					(210)	210
Balance at Mar. 31, 2018	436,926	$ 87	$ 30	394,313	(1,509)	44,005
Balance (in shares) at Mar. 31, 2018		8,700,000	3,018,000
Balance at Dec. 30, 2017	423,523	$ 86	$ 30	372,590	(1,288)	52,105
Balance (in shares) at Dec. 30, 2017		8,603,000	3,018,000
Net income	32,845
Currency translation adjustment	(18)
Balance at Jun. 30, 2018	442,672	$ 86	$ 30	399,616	(1,516)	44,456
Balance (in shares) at Jun. 30, 2018		8,635,000	3,018,000
Balance at Mar. 31, 2018	436,926	$ 87	$ 30	394,313	(1,509)	44,005
Balance (in shares) at Mar. 31, 2018		8,700,000	3,018,000
Net income	23,535					23,535
Stock options exercised and restricted shares activities (in shares)		32,000
Stock options exercised and restricted shares activities	2,224			2,224
Stock-based compensation expense	3,079			3,079
Repurchase of Class A Common Stock (in shares)		(97,000)
Repurchase of Class A Common Stock	(23,085)	$ (1)				(23,084)
Currency translation adjustment	(7)				(7)
Balance at Jun. 30, 2018	442,672	$ 86	$ 30	399,616	(1,516)	44,456
Balance (in shares) at Jun. 30, 2018		8,635,000	3,018,000
Balance at Dec. 29, 2018	460,317	$ 86	$ 29	405,711	(1,197)	55,688
Balance (in shares) at Dec. 29, 2018		8,580,000	2,918,000
Net income	23,694					23,694
Stock options exercised and restricted shares activities (in shares)		54,000
Stock options exercised and restricted shares activities	3,704			3,704
Stock-based compensation expense	2,066			2,066
Currency translation adjustment	37				37
Balance at Mar. 30, 2019	489,818	$ 86	$ 29	411,481	(1,160)	79,382
Balance (in shares) at Mar. 30, 2019		8,634,000	2,918,000
Balance at Dec. 29, 2018	460,317	$ 86	$ 29	405,711	(1,197)	55,688
Balance (in shares) at Dec. 29, 2018		8,580,000	2,918,000
Net income	$ 51,550
Stock options exercised and restricted shares activities (in shares)	43,866
Currency translation adjustment	$ (42)
Balance at Jun. 29, 2019	522,801	$ 87	$ 29	416,602	(1,155)	107,238
Balance (in shares) at Jun. 29, 2019		8,655,000	2,918,000
Balance at Mar. 30, 2019	489,818	$ 86	$ 29	411,481	(1,160)	79,382
Balance (in shares) at Mar. 30, 2019		8,634,000	2,918,000
Net income	27,856					27,856
Stock options exercised and restricted shares activities (in shares)		21,000
Stock options exercised and restricted shares activities	1,378	$ 1		1,377
Stock-based compensation expense	3,744			3,744
Currency translation adjustment	(5)				5
Balance at Jun. 29, 2019	$ 522,801	$ 87	$ 29	$ 416,602	$ (1,155)	$ 107,238
Balance (in shares) at Jun. 29, 2019		8,655,000	2,918,000