Computation of Earnings Per Share, Basic (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 30, 2013		Mar. 31, 2012
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 6,912		$ 7,493
Allocation of net income for basic:
Allocation of net income for basic common stock	6,912		7,493
Allocation of net income for basic unvested participating shares	51
Weighted average number of shares for basic:
Weighted average number of shares for basic unvested participating shares	97
Shares used in net income per common share - basic	12,908		12,759
Net income per share for basic:
Net Income Per Common Stock	$ 0.54		$ 0.59
Common Class A
Allocation of net income for basic:
Allocation of net income for basic common stock	4,664		5,081
Weighted average number of shares for basic:
Weighted average number of shares for basic common stock	8,709		8,652
Net income per share for basic:
Net Income Per Common Stock	$ 0.54		$ 0.59
Common Class B
Allocation of net income for basic:
Allocation of net income for basic common stock	$ 2,197		$ 2,412
Weighted average number of shares for basic:
Weighted average number of shares for basic common stock	4,102	[1]	4,107	[1]
Net income per share for basic:
Net Income Per Common Stock	$ 0.54		$ 0.59

[1] Change in Class B Common Stock resulted from the conversion of 100,000 shares to Class A Common Stock on March 25, 2013, weighted average for the period.