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. 30, 2012	Jun. 25, 2011	Jun. 30, 2012	Jun. 25, 2011
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
As reported-basic	$ 14,351	$ 28,019	$ 21,844	$ 31,978
Add: effect of dilutive potential common shares
As reported-basic	12,790	13,223	12,774	13,249
Add: effect of dilutive potential common shares
Net income per common share-diluted	13,437	13,947	13,428	13,977
As reported - basic	$ 1.11	$ 2.12	$ 1.69	$ 2.41
Net income per common share-diluted	$ 1.06	$ 2.01	$ 1.61	$ 2.29
Common Class A
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
As reported-basic	9,652	19,316	14,683	22,065
Add: effect of dilutive potential common shares
Class B Common Stock	4,566	8,703	6,958	9,913
Net effect of unvested participating shares	6		10
Net income per common share-diluted	$ 14,224	$ 28,019	$ 21,651	$ 31,978
As reported-basic	8,683	9,116	8,667	9,142
Add: effect of dilutive potential common shares
Share-based awards	647	724	654	728
Class B Common Stock	4,107	4,107	4,107	4,107
Net income per common share-diluted	13,437	13,947	13,428	13,977
As reported - basic	$ 1.11	$ 2.12	$ 1.69	$ 2.41
Net income per common share-diluted	$ 1.06	$ 2.01	$ 1.61	$ 2.29