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Stock Based Compensation (Details) (USD $)
 3 Months Ended 9 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2012
Sep. 30, 2011
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 $ 10,439,000 $ 7,660,000 $ 30,143,000 $ 23,466,000
Tax effect recognized in net income 3,654,000 2,681,000 10,550,000 8,216,000
Windfall tax benefit/(shortfall), net 9,009,000 372,000 19,975,000 3,999,000
Employee stock options granted during the period     531,100 753,500
Weighted average assumptions used to value option grants Table        
Fair value per share ($)     $ 30.19 $ 24.45
Risk-free interest rate (%)     0.77% 1.91%
Expected option life (years)     5 years 2 months 26 days 5 years 4 months 2 days
Expected volatility (%)     36.51% 35.26%
Expected dividend yield (%)     0.58% 0.60%
Cash received from exercise of options     40,105,000 14,479,000
Restricted stock awards granted during period     358,807 339,330
Weighted average fair value per share of restricted stock awards granted during the period     $ 95.10 $ 74.27
Restricted stock awards vested during period     205,405  
Weighted average grant date fair value per share     $ 55.98  
Weighted average vest date fair value per share     $ 94.57  
Shares of stock purchased during the period by participants in the employee stock purchase plan     17,410 20,628
Amount paid for stock purchased during the period by participants in the employee stock purchase plan     $ 1,600,000 $ 1,600,000