Computation of Diluted Net Income Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 28, 2014	Jun. 29, 2013	Jun. 28, 2014	Jun. 29, 2013
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
As reported - basic	$ 25,428	$ 19,715	$ 33,743	$ 26,627
Add: effect of dilutive potential common shares
Net income per common share - diluted	13,486	13,462	13,461	13,484
As reported - basic	$ 1.95	$ 1.53	$ 2.59	$ 2.07
Net income per common share - diluted	$ 1.88	$ 1.45	$ 2.49	$ 1.96
Common Class A
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
As reported - basic	17,935	13,431	23,600	18,053
Add: effect of dilutive potential common shares
Class B Common Stock	7,353	6,141	9,955	8,378
Net effect of unvested participating shares	5	7	7	10
Net income per common share - diluted	$ 25,293	$ 19,579	$ 33,562	$ 26,441
As reported - basic	9,196	8,765	9,097	8,737
Add: effect of dilutive potential common shares
Share-based awards	520	690	527	692
Class B Common Stock	3,770	4,007	3,837	4,055
Net income per common share - diluted	13,486	13,462	13,461	13,484
As reported - basic	$ 1.95	$ 1.53	$ 2.59	$ 2.07
Net income per common share - diluted	$ 1.88	$ 1.45	$ 2.49	$ 1.96