Schedule of Information on Non - Vested Restricted Stock Units (Detail) - Non Vested Restricted Stock and Deferred Stock Units	9 Months Ended
Sep. 26, 2020 $ / shares shares
Number of Shares and Deferred Stock Units
Beginning Balance \| shares	64,808
Granted \| shares	26,604
Vested \| shares	(28,621)
Forfeited \| shares	(2,351)
Ending Balance \| shares	60,440
Weighted Average Grant Date Fair Value
Beginning Balance \| $ / shares	$ 98.24
Granted \| $ / shares	111.88
Vested \| $ / shares	98.83
Forfeited \| $ / shares	106.34
Ending Balance \| $ / shares	$ 103.65

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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