Equity Awards - Stock Option Activity Table (Details) (USD $)	3 Months Ended
Mar. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Options Outstanding, beginning balance	675,665
Number of Options Exercised	(170,050)
Number of Options Cancelled	0
Number of Options Expired	0
Number of Options Outstanding, ending balance	505,615
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Options Outstanding, Weighted Average Price, beginning	$ 15.52
Options Exercised, Weighted Average Price	$ 22.21
Options Cancelled, Weighted Average Price	$ 0.00
Options Expired, Weighted Average Price	$ 0.00
Options Outstanding, Weighted Average Price, ending	$ 13.27
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures
Options Average Remaining Contractual Life (Years)	4 years 1 month
Options Aggregate Intrinsic Value	$ 9,709,312

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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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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 of the plan that expired.

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

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