Computation of Basic and Diluted Net Income Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 26, 2011
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Net income	$ 7,493	$ 3,959
Shares used in net income per common share - basic	12,759	13,274
Dilutive potential common shares	690	733
Shares used in net income per common share - diluted	13,449	14,007
Net income per common share - basic	$ 0.59	$ 0.30
Net income per common share - diluted	$ 0.56	$ 0.28
Employee Stock Option
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Effect of dilutive securities	661	685
Restricted Stock Awards
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Effect of dilutive securities	29	48
Common Class A
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Shares used in net income per common share - basic	8,652	9,167
Common Class B
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Shares used in net income per common share - basic	4,107	4,107