Stock Based Compensation - Options Rollforward (Details) (USD $)	3 Months Ended
Mar. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning Balance	107,455
Options Granted	29,302
Options Exercised	(20,433)
Options Forfeited	(3,601)
Ending Balance	112,723
Options Exerciseable	48,581
Weighted Average Exercise Price [Abstract]
Outstanding at Beginning of Year	$ 31.23
Options Granted	$ 58.26
Options Exercised	$ 25.46
Options Forfeited	$ 37.81
Outstanding at End of Period	$ 39.09
Options Exercisable	$ 28.01
Weighted Average Contractual Term [Abstract]
Weighted Average Remaining Contractual Term, Outstanding	5 years 6 months
Weighted Average Remaining Contractual Term, Exercisable	4 years 6 months

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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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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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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

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No definition available.

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The number of shares reserved for issuance under stock option agreements awarded under the plan that validly exist and are outstanding as of the balance sheet date, including vested options.

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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 remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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 price at which grantees can acquire the shares reserved for issuance on stock options awarded.

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

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