Share-Based Compensation (Summary of Stock Option Activity) (Details) - $ / shares	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Shares [Roll Forward]
Outstanding, beginning of period (in shares)	2,445,849
Granted (in shares)	1,933,920
Exercised (in shares)	(146,114)
Forfeited or Expired (in shares)	(58,198)
Outstanding, end of period (in shares)	4,175,457
Exercisable, end of period (in shares)	683,489	560,848
Weighted Average Exercise Price [Roll Forward]
Outstanding, beginning of period (weighted average exercise price)	$ 30.77
Granted (weighted average exercise price)	41.36
Exercised (weighted average exercise price)	27.43
Forfeited or Expired (weighted average exercise price)	34.33
Outstanding, end of period (weighted average exercise price)	35.74
Exercisable, end of period (weighted average exercise price)	$ 26.11	$ 18.67

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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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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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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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 per share amount at which grantees can acquire shares of common stock by exercise of options.

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The number of shares reserved for issuance pertaining to the outstanding exercisable stock options as of the balance sheet date in the customized range of exercise prices for which the market and performance vesting condition has been satisfied.

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Weighted average exercise price as of the balance sheet date for those equity-based payment arrangements exercisable and outstanding.

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

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