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. 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
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
Balance at Dec. 28, 2019	735,636	$ 94	$ 27	571,784	(1,669)	165,400
Balance (in shares) at Dec. 28, 2019		9,371,000	2,673,000
Net income	18,234					18,234
Stock options exercised and restricted shares activities (in shares)		38,000
Stock options exercised and restricted shares activities	1,858			1,858
Stock-based compensation expense	2,566			2,566
Conversion from Class B to Class A (in shares)		150,000	(150,000)
Conversion from Class B to Class A		$ 2	$ (2)
Currency translation adjustment	(58)				(58)
Balance at Mar. 28, 2020	758,236	$ 96	$ 25	576,208	(1,727)	183,634
Balance (in shares) at Mar. 28, 2020		9,559,000	2,523,000
Balance at Dec. 28, 2019	735,636	$ 94	$ 27	571,784	(1,669)	165,400
Balance (in shares) at Dec. 28, 2019		9,371,000	2,673,000
Net income	$ 78,375
Stock options exercised and restricted shares activities (in shares)	57,926
Currency translation adjustment	$ (71)
Balance at Jun. 27, 2020	827,483	$ 98	$ 23	585,327	(1,740)	243,775
Balance (in shares) at Jun. 27, 2020		9,835,000	2,308,000
Balance at Mar. 28, 2020	758,236	$ 96	$ 25	576,208	(1,727)	183,634
Balance (in shares) at Mar. 28, 2020		9,559,000	2,523,000
Net income	60,141					60,141
Stock options exercised and restricted shares activities (in shares)		61,000
Stock options exercised and restricted shares activities	4,582			4,582
Stock-based compensation expense	4,537			4,537
Conversion from Class B to Class A (in shares)		215,000	(215,000)
Conversion from Class B to Class A		$ 2	$ (2)
Currency translation adjustment	(13)				(13)
Balance at Jun. 27, 2020	$ 827,483	$ 98	$ 23	$ 585,327	$ (1,740)	$ 243,775
Balance (in shares) at Jun. 27, 2020		9,835,000	2,308,000