Share-Based Compensation - Stock Option Activity (Details) - $ / shares shares in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Number of Options (in thousands)
Beginning balance (in shares)	3,610	4,013	3,879
Granted (in shares)	493	535	731
Exercised (in shares)	(598)	(908)	(597)
Forfeited (in shares)	(4)	(30)
Ending balance (in shares)	3,501	3,610	4,013
Weighted Average Exercise Price per Option
Weighted average beginning balance (in dollars per share)	$ 46.44	$ 41.13	$ 36.05
Granted (in dollars per share)	76.16	67.23	57.34
Exercised (in dollars per share)	38.96	34.84	27.97
Forfeited (in dollars per share)	77.58	58.01
Weighted average ending balance (in dollars per share)	$ 51.87	$ 46.44	$ 41.13

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- Definition

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

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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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- 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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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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