Income Taxes (Details 2) (USD $)	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Income Taxes
Excess tax benefit from exercise of stock options	$ 3,021,000	$ 5,500,000
Net unrecognized tax benefits	2,200,000	1,400,000
Accrued liabilities for interest and penalties related to uncertain tax positions	900,000	600,000
Reasonably possible decrease in unrecognized tax benefits within the next year	$ 100,000

Tax benefit associated with any equity-based compensation plan other than an employee stock ownership plan (ESOP). The tax benefit results from the deduction by the entity on its tax return for an award of stock that exceeds the cumulative compensation cost for common stock or preferred stock recognized for financial reporting. Includes any resulting tax benefit that exceeds the previously recognized deferred tax asset (excess tax benefits).

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This element represents the total of accruals as of the date of the statement of financial position for interest recognized for an underpayment of income taxes computed by applying the applicable statutory rate of interest to the difference between a tax position recognized for financial reporting purposes and the amount previously taken or expected to be taken in a tax return of the entity and the amount of statutory penalties for a tax position claimed or expected to be claimed by the entity, in its tax return, that does not meet the minimum statutory threshold to avoid payment of penalties.

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