Computation of Diluted Net Income Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 30, 2013	Mar. 31, 2012
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
As reported - basic	$ 6,912	$ 7,493
Add: effect of dilutive potential common shares
Net income per common share - diluted	13,505	13,449
As reported - basic	$ 0.54	$ 0.59
Net income per common share - diluted	$ 0.51	$ 0.56
Common Class A
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
As reported - basic	4,664	5,081
Add: effect of dilutive potential common shares
Class B Common Stock	2,197	2,412
Net effect of unvested participating shares	2
Net income per common share - diluted	$ 6,863	$ 7,493
As reported - basic	8,709	8,652
Add: effect of dilutive potential common shares
Share-based awards	694	690
Class B Common Stock	4,102	4,107
Net income per common share - diluted	13,505	13,449
As reported - basic	$ 0.54	$ 0.59
Net income per common share - diluted	$ 0.51	$ 0.56