Stock Plans - Stock Option Activity (Details) - $ / shares shares in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Number of Shares
Outstanding at the beginning of the period (in shares)	1,222	1,394	1,576
Exercised (in shares)			(18)
Expired or forfeited (in shares)	(103)	(172)	(164)
Outstanding at the end of the period (in shares)	1,119	1,222	1,394
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 34.80	$ 34.97	$ 35.18
Exercised (in dollars per share)			30.03
Expired or forfeited (in dollars per share)	33.97	36.21	37.47
Outstanding at the end of the period (in dollars per share)	$ 34.88	$ 34.80	$ 34.97

No definition available.

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- Definition

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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- Definition

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

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- Definition

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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- Definition

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

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