Computation of Diluted Net Income Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 30, 2019	Mar. 31, 2018
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Allocation of net income for basic common stock	$ 23,694	$ 9,310
Add: effect of dilutive potential common shares Share-based awards	112	99
Earnings to Common Shareholders, Net effect of unvested participating shares	$ 2	$ 1
Earnings to Common Shareholders, Net income per common share — diluted	$ 23,469	$ 9,253
Weighted-average number of common shares — basic	11,635	11,805
Weighted-average number of common shares — diluted	11,636	11,831
Net income per common share — basic	$ 2.04	$ 0.79
Net income per common share — diluted	$ 2.02	$ 0.78
Common Class A
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Allocation of net income for basic common stock	$ 17,525	$ 6,872
Weighted-average number of common shares — basic	8,606	8,714
Net income per common share — basic	$ 2.04	$ 0.79
Common Class B
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Allocation of net income for basic common stock	$ 5,942	$ 6,872
Class B Common Stock	2,918	3,018
Earnings to Common Shareholders, Class B Common Stock	$ 5,942	$ 2,380
Weighted-average number of common shares — basic	2,918	3,018
Net income per common share — basic	$ 2.04	$ 0.79