Shareholders' Equity and Share-Based Compensation - Non-vested stock activity (Details) - $ / shares shares in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 26, 2019	Dec. 27, 2018
Shareholders' Equity and Share-Based Compensation
Shares, Outstanding at beginning of year	174	158	137
Shares, Granted	42	39	52
Shares, Vested	(69)	(23)	(31)
Shares, Forfeited	0
Shares, Outstanding at end of year	147	174	158
Weighted- Average Fair Value, Outstanding at beginning of year	$ 29.16	$ 18.98	$ 21.94
Weighted- Average Fair Value, Granted	31.43	38.24	29.02
Weighted- Average Fair Value, Vested	26.56	18.60	16.41
Weighted- Average Fair Value, Forfeited	0
Weighted- Average Fair Value, Outstanding at end of year	$ 31.02	$ 29.16	$ 18.98

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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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