Computation of Earnings Per Share, Basic (Detail) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
 3 Months Ended
Mar. 26, 2016
Mar. 28, 2015
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]    
Net Income $ 7,032 $ 13,743
Allocation of net income for basic:    
Allocation of net income for basic common stock 7,032 13,743
Allocation of net income for basic unvested participating shares $ 34 $ 65
Weighted average number of shares for basic:    
Weighted average number of shares for basic unvested participating shares 62 63
Shares used in net income per common share - basic 12,804 13,278
Net income per share for basic:    
Net income per common share - basic $ 0.55 $ 1.04
Common Class A    
Allocation of net income for basic:    
Allocation of net income for basic common stock $ 5,149 $ 9,934
Weighted average number of shares for basic:    
Weighted-average number of common shares - basic 9,375 9,598
Net income per share for basic:    
Net income per common share - basic $ 0.55 $ 1.04
Common Class B    
Allocation of net income for basic:    
Allocation of net income for basic common stock $ 1,849 $ 3,744
Weighted average number of shares for basic:    
Weighted-average number of common shares - basic [1] 3,367 3,617
Net income per share for basic:    
Net income per common share - basic $ 0.55 $ 1.04
[1] Change in Class B Common Stock resulted from the conversion of 150,000 shares to Class A Common Stock on May 6, 2015 and 100,000 shares to Class A Common Stock on October 26, 2015, with the thirteen-week number of shares reflecting the weighted average for the periods.