Computation of Diluted Net Income Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 26, 2016	Mar. 28, 2015
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Allocation of net income for basic common stock	$ 7,032	$ 13,743
Weighted-average number of common shares - diluted	13,088	13,633
Net income per common share - basic	$ 0.55	$ 1.04
Net income per common share - diluted	$ 0.53	$ 1.00
Common Class A
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Allocation of net income for basic common stock	$ 5,149	$ 9,934
Allocation of net income to Class B Common Stock	1,849	3,744
Net effect of unvested participating shares	1	2
Net Income for diluted common stock	$ 6,999	$ 13,680
Weighted-average number of common shares - basic	9,375	9,598
Add: effect of dilutive potential common share-based awards	346	418
Weighted average number of shares of Class B Common Stock	3,367	3,617
Weighted-average number of common shares - diluted	13,088	13,633
Net income per common share - basic	$ 0.55	$ 1.04
Net income per common share - diluted	$ 0.53	$ 1.00