Share-Based Compensation Option Activity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Shares
Beginning Balance	1,811,536	1,943,485
Granted	0	0
Exercised	(226,068)	(114,634)
Forfeited	0	(17,315)
Ending Balance	1,585,468	1,811,536	1,943,485
Weighted Average Exercise Price
Beginning Balance	$ 11.41	$ 11.16
Granted	$ 0	$ 0.00
Exercised	$ 9.59	$ 7.34
Forfeited	$ 0.00	$ 9.89
Ending Balance	$ 11.67	$ 11.41	$ 11.16
Remaining Average Contractual Term (Year) and Aggregate Intrinsic Value
Weighted Average Remaining Contractual Term (Years)	3 years 9 months 18 days	4 years 9 months 18 days	5 years 9 months 18 days
Aggregate Intrinsic Value	$ 10,258	$ 4,927	$ 6,414

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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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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of options outstanding.

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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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