Stock-Based Compensation (Schedule of Option Share Awards) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended
Sep. 30, 2011
Stock-Based Compensation
Shares outstanding, beginning balance	1,806,110
Exercised	(496,754)
Shares outstanding, ending balance	1,309,356
Weighted average exercise price, beginning of period	$ 30.96
Exercised	$ 29.04
Weighted average exercise price, end of period	$ 31.69
Weighted average remaining contractual term (in years)	2.1
Aggregate intrinsic value at end of period	$ 4,533

As of the balance sheet date, the total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices of options outstanding.

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The weighted average price at which option holders acquired shares when converting their stock options into shares under the plan during the reporting period.

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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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The weighted average price as of the beginning of the year at which grantees can acquire the shares reserved for issuance under the stock option plan.

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The weighted average period between the balance sheet date and expiration for all awards outstanding under the plan, which may be expressed in a decimal value for number of years.

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

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