Stock-Based Compensation - Changes in Stock Options (Details) - $ / shares	9 Months Ended
Sep. 23, 2020
Shares
Outstanding-beginning balance (shares)	2,077,570
Exercised (shares)	(965,736)
Forfeited, cancelled or expired (shares)	(75,968)
Outstanding-ending balance (shares)	1,035,866
Vested and expected to vest at end of period (shares)	1,030,329
Exercisable at end of period (shares)	689,166
Weighted-Average Exercise Price
Outstanding-beginning balance (usd per share)	$ 8.14
Exercised (usd per share)	6.05
Forfeited, cancelled or expired (usd per share)	12.14
Outstanding-ending balance (usd per share)	9.79
Vested and expected to vest at end of period (usd per share)	9.78
Exercisable at end of period (usd per share)	$ 8.98

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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- Definition

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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For presentations that combine terminations, 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 or that expired.

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Weighted average price of options that were either forfeited or expired.

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

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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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 exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest exercisable or convertible options. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of fully vested and expected to vest options outstanding that can be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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

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

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