Computation of Earnings Per Share, Basic (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended										12 Months Ended
		Dec. 30, 2017	[1]	Sep. 30, 2017	Jul. 01, 2017	Apr. 01, 2017	Dec. 31, 2016	[2]	Sep. 24, 2016	Jun. 25, 2016	Mar. 26, 2016	Dec. 30, 2017	Dec. 31, 2016	Dec. 26, 2015
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income		$ 30,530		$ 33,683	$ 29,125	$ 5,711	$ 22,166		$ 31,530	$ 26,621	$ 7,032	$ 99,049	$ 87,349	$ 98,414
Allocation of net income for basic:
Allocation of net income for basic common stock												99,049	87,349	98,414
Allocation of net income for basic unvested participating shares												$ 544	$ 442	$ 462
Weighted average number of shares for basic:
Weighted average number of shares for basic unvested participating shares												67	64	62
Shares used in net income per common share - basic												12,102	12,597	13,185
Net income per share for basic:
Net income per common share - basic		$ 2.60		$ 2.82	$ 2.38	$ 0.46	$ 1.77		$ 2.53	$ 2.11	$ 0.55	$ 8.18	$ 6.93	$ 7.46
Common Class A
Allocation of net income for basic:
Allocation of net income for basic common stock												$ 73,114	$ 63,717	$ 71,798
Weighted average number of shares for basic:
Weighted-average number of common shares - basic												8,933	9,189	9,619
Net income per share for basic:
Net income per common share - basic												$ 8.18	$ 6.93	$ 7.46
Common Class B
Allocation of net income for basic:
Allocation of net income for basic common stock												$ 25,391	$ 23,190	$ 26,154
Weighted average number of shares for basic:
Weighted-average number of common shares - basic	[3]											3,102	3,344	3,504
Net income per share for basic:
Net income per common share - basic												$ 8.18	$ 6.93	$ 7.46

[1] During the fourth quarter of 2017, the Company recorded a $20.3 million tax benefit due to the Tax Cuts and Jobs Act of 2017.

[2] During the fourth quarter of 2016, the Company recorded a $3.6 million decrease in stock-based compensation expense related to the planned retirement of the Company's Chief Executive Officer in 2018.

[3] Change in Class B Common Stock resulted from the conversion of 125,000 shares to Class A Common Stock on November 4, 2016, 45,000 shares to Class A Common Stock on November 30, 2016, 100,000 shares to Class A Common Stock on March 7, 2017, and 79,000 shares to Class A Common Stock on October 31, 2017 with the ending number of shares reflecting the weighted average for the period.