Pension Plan Asset by Category and Level (Detail) - USD ($) $ in Thousands		Dec. 24, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		$ 19,664	$ 18,510
Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	19,664	12,723
U.S. Large Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]		1,123
U.S. Mid Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]		1,118
U.S. Small Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]		1,118
International
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]		1,685
Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[3]		743
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		19,662	5,787
Level 1 | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	19,662
Level 1 | U.S. Large Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]		1,123
Level 1 | U.S. Mid Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]		1,118
Level 1 | U.S. Small Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]		1,118
Level 1 | International
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]		1,685
Level 1 | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[3]		743
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		2	12,723
Level 2 | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	$ 2	$ 12,723

[1] Cash and cash equivalents, which are used to pay benefits and administrative expenses, are held in money market and stable value fund.

[2] Equity securities consist of mutual funds and the underlying investments are indexes. Investments in mutual funds are valued at the net asset value per share multiplied by the number of shares held.

[3] Fixed income securities consist of bonds securities in mutual funds, and are valued at the net asset value per share multiplied by the number of shares held.