Employee Benefit Plans - Summary of transactions involving stock options (Details) (Stock Options, USD $)	12 Months Ended
Dec. 31, 2012
Stock Options
Shares
Outstanding at January 1, 2012	704,689
Granted
Exercised	704,689
Forfeited
Expired
Outstanding and exercisable at December 31, 2012
Weighted Average Exercise Price
Outstanding at January 1, 2012	$ 1.31
Granted
Exercised	$ 1.31
Forfeited
Expired
Outstanding and exercisable at December 31, 2012
Weighted Average Remaining Contractual Life
Weighted Average Remaining Contractual Life, Outstanding at January 1, 2012	0.99 years

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Weighted average remaining contractual term for option awards outstanding.

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Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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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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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 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 of the plan that expired.

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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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