Stock-based Compensation (Summary of Stock Option Activity) (Details) - $ / shares	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Shares
Outstanding, beginning of period, Shares	1,099,076	1,062,177
Granted, Shares	232,568	291,390
Exercised, Shares	(64,017)	(84,353)
Forfeited or cancelled, Shares	(3,141)	(50,491)
Outstanding, end of period, Shares	1,264,486	1,218,723
Weighted Average Exercise Price
Outstanding, beginning of period, Weighted Average Exercise Price	$ 85.75	$ 75.53
Granted, Weighted Average Exercise Price	95.05	110.58
Exercised, Weighted Average Exercise Price	75.98	70.31
Forfeited or cancelled, Weighted Average Exercise Price	95.39	88.48
Outstanding, end of period, Weighted Average Exercise Price	$ 87.93	$ 83.73

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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Gross 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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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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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Number of share options (or share units) exercised during the current period.

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