Stockholders' Equity (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	9 Months Ended
Sep. 30, 2012
Summary of stock option activity
Outstanding at December 31, 2011	2,130
Weighted Average Exercise Price, Beginning Balance	$ 27.46
Granted	(381)
Weighted Average Exercise Price, Granted	$ 33.84
Exercised	(323)
Weighted Average Exercise Price ,Exercised	$ 24.72
Forfeited	105
Weighted Average Exercise Price, Forfeited	$ 30.91
Outstanding at September 30, 2012	2,083
Weighted Average Exercise Price, Ending Balance	$ 28.88
Weighted Average Remaining Contractual Term, Outstanding	6 years 5 months 5 days
Aggregate Intrinsic Value, Outstanding, Ending Balance	$ 4,339
Exercisable at September 30, 2012	1,202
Weighted Average Exercise Price per share, exercisable	$ 26.19
Weighted Average Remaining Contractual Term, Exercisable	4 years 9 months 7 days
Aggregate Intrinsic Value, Exercisable	$ 3,973

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

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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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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 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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