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Stock Based Compensation (Details) (USD $)
In Thousands, except Share data, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2011
Jun. 30, 2010
Jun. 30, 2011
Jun. 30, 2010
Notes to Financial Statements [Abstract]        
Percentage of eligible earnings to purchase common stock through the employee stock purchase plan 10.00%   10.00%  
Discount on the average closing price for the employee stock purchase plan     5.00%  
Stock Based Compensation Expense Table        
Stock based compensation $ 7,700 $ 6,100 $ 15,800 $ 13,100
Tax effect recognized in net income 2,700 2,100 5,500 4,600
Windfall tax benefit/(shortfall), net 900 1,800 3,700 2,900
Employee stock options granted during the period     652,000 573,350
Weighted average assumptions used to value option grants Table        
Fair value per share ($)     $ 24.86 $ 16.84
Risk-free interest rate (%)     2.07% 2.36%
Expected option life (years)     5.33 5.38
Expected volatility (%)     35.17% 34.54%
Expected dividend yield (%)     0.59% 0.72%
Cash received from exercise of options     12,914 8,489
Restricted stock awards granted during period     310,580 250,243
Weighted average fair value per share of restricted stock awards granted during the period     $ 74.76 $ 52.55
Restricted stock awards vested during period     211,101  
Weighted average grant date fair value per share     $ 51.85  
Weighted average vest date fair value per share     $ 76.54  
Shares of stock purchased during the period by participants in the employee stock purchase plan     13,356 14,538
Amount paid for stock purchased during the period by participants in the employee stock purchase plan     $ 1,060 $ 780