Shareholders' Equity and Share-Based Compensation - Stock option activity (Details) - $ / shares shares in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 26, 2019	Dec. 27, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding
Outstanding at beginning of period	1,641	1,450	1,629
Granted	728	329	336
Exercised	(31)	(97)	(478)
Forfeited	(104)	(41)	(37)
Outstanding at end of period	2,234	1,641	1,450
Exercisable at end of period	1,001	802	699
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price
Outstanding at beginning of period	$ 25.46	$ 21.25	$ 18.08
Granted	23.47	41.67	27.59
Exercised	12.21	15.60	14.74
Forfeited	28.06	30.58	23.35
Outstanding at end of period	24.87	25.46	21.25
Exercisable at end of period	20.38	18.22	15.87
Weighted-average fair value of options granted during the period	$ 5.96	$ 11.79	$ 7.87

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Gross number of share options (or share units) granted during the period.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Number of options outstanding, including both vested and non-vested options.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Number of share options (or share units) exercised during the current period.

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