Computation of Earnings Per Share, Basic (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 28, 2015	Mar. 29, 2014
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net Income	$ 13,743	$ 8,315
Allocation of net income for basic:
Allocation of net income for basic unvested participating shares	65	47
Allocation of net income for basic common stock	13,743	8,315
Weighted average number of shares for basic:
Weighted average number of shares for basic unvested participating shares	63	73
Shares used in net income per common share - basic	13,278	12,977
Net income per share for basic:
Net Income Per Common Stock	$ 1.04	$ 0.64
Common Class A
Allocation of net income for basic:
Allocation of net income for basic common stock	9,934	5,766
Weighted average number of shares for basic:
Weighted average number of shares for basic common stock	9,598	8,999
Net income per share for basic:
Net Income Per Common Stock	$ 1.04	$ 0.64
Common Class B
Allocation of net income for basic:
Allocation of net income for basic common stock	$ 3,744	$ 2,502
Weighted average number of shares for basic:
Weighted average number of shares for basic common stock	3,617	3,905
Net income per share for basic:
Net Income Per Common Stock	$ 1.04	$ 0.64