Computation of Diluted Net Income Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 25, 2016	Jun. 27, 2015	Jun. 25, 2016	Jun. 27, 2015
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Allocation of net income for basic common stock	$ 26,621	$ 29,932	$ 33,653	$ 43,675
Weighted-average number of common shares-diluted	12,830	13,667	12,959	13,650
Net income per common share-basic	$ 2.11	$ 2.24	$ 2.65	$ 3.28
Net income per common share-diluted	$ 2.06	$ 2.18	$ 2.58	$ 3.18
Common Class A
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Allocation of net income for basic common stock	$ 19,375	$ 21,870	$ 24,567	$ 31,740
Allocation of net income to Class B Common Stock	7,107	7,923	8,916	11,729
Net effect of unvested participating shares	3	4	4	6
Net Income for diluted common stock	$ 26,485	$ 29,797	$ 33,487	$ 43,475
Weighted-average number of common shares-basic	9,181	9,748	9,278	9,673
Add: effect of dilutive potential common share-based awards	282	387	314	402
Weighted average number of shares of Class B Common Stock	3,367	3,532	3,367	3,575
Weighted-average number of common shares-diluted	12,830	13,667	12,959	13,650
Net income per common share-basic	$ 2.11	$ 2.24	$ 2.65	$ 3.28
Net income per common share-diluted	$ 2.06	$ 2.18	$ 2.58	$ 3.18