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Income Taxes (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2010
Jun. 30, 2011
Jun. 30, 2010
Dec. 31, 2009
years
Dec. 31, 2008
years
Income Taxes          
Effective tax rate (as a percent)   36.80%      
Estimated annual effective tax rate percentage (as a percent)   36.80% 36.20%    
Net operating loss carryback provision term before change in law (in years)       2 2
Net operating loss carryback provision term after change in law (in years)       5 5
Income tax refunds $ 121.5