Computation of Diluted Net Income Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 29, 2014	Mar. 30, 2013
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
As reported - basic	$ 8,315	$ 6,912
Add: effect of dilutive potential common shares
Net income per common share - diluted	13,435	13,505
As reported - basic	$ 0.64	$ 0.54
Net income per common share - diluted	$ 0.62	$ 0.51
Common Class A
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
As reported - basic	5,766	4,664
Add: effect of dilutive potential common shares
Class B Common Stock	2,502	2,197
Net effect of unvested participating shares	2	2
Net income per common share - diluted	$ 8,270	$ 6,863
As reported - basic	8,999	8,709
Add: effect of dilutive potential common shares
Share-based awards	531	694
Class B Common Stock	3,905	4,102
Net income per common share - diluted	13,435	13,505
As reported - basic	$ 0.64	$ 0.54
Net income per common share - diluted	$ 0.62	$ 0.51