Computation of Earnings Per Share, Basic (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 29, 2019	Mar. 30, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 29, 2019	Jun. 30, 2018
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 27,856	$ 23,694	$ 23,535	$ 9,310	$ 51,550	$ 32,845
Allocation of net income for basic:
Allocation of net income for basic common stock	27,856		17,290		51,550	32,845
Allocation of net income for basic unvested participating shares	$ 253		$ 225		$ 481	$ 258
Weighted average number of shares for basic:
Weighted-average number of common shares — basic	11,672		11,797		11,654	11,801
Net income per share for basic:
Net income per common share — basic	$ 2.39		$ 1.99		$ 4.42	$ 2.78
Common Class A
Allocation of net income for basic:
Allocation of net income for basic common stock	$ 20,639		$ 17,290		$ 38,161	$ 24,187
Weighted average number of shares for basic:
Weighted-average number of common shares — basic	8,648		8,667		8,627	8,690
Net income per share for basic:
Net income per common share — basic	$ 2.39		$ 1.99		$ 4.42	$ 2.78
Common Class B
Allocation of net income for basic:
Allocation of net income for basic common stock	$ 6,964		$ 6,020		$ 12,908	$ 8,400
Weighted average number of shares for basic:
Weighted-average number of common shares — basic	2,918		3,018		2,918	3,018
Net income per share for basic:
Net income per common share — basic	$ 2.39		$ 1.99		$ 4.42	$ 2.78
Unvested participating shares
Weighted average number of shares for basic:
Weighted-average number of common shares — basic	106		112		109	93