Computation of Earnings Per Share, Basic (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 30, 2019	Mar. 31, 2018
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 23,694	$ 9,310
Allocation of net income for basic:
Allocation of net income for basic common stock	23,694	9,310
Allocation of net income for basic unvested participating shares	$ 227	$ 58
Weighted average number of shares for basic:
Weighted-average number of common shares — basic	11,635	11,805
Net income per share for basic:
Net income per common share — basic	$ 2.04	$ 0.79
Common Class A
Allocation of net income for basic:
Allocation of net income for basic common stock	$ 17,525	$ 6,872
Weighted average number of shares for basic:
Weighted-average number of common shares — basic	8,606	8,714
Net income per share for basic:
Net income per common share — basic	$ 2.04	$ 0.79
Common Class B
Allocation of net income for basic:
Allocation of net income for basic common stock	$ 5,942	$ 6,872
Weighted average number of shares for basic:
Weighted-average number of common shares — basic	2,918	3,018
Net income per share for basic:
Net income per common share — basic	$ 2.04	$ 0.79
Unvested participating shares
Weighted average number of shares for basic:
Weighted-average number of common shares — basic	111	73