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Summary Of Significant Accounting Policies (Assumptions Used To Estimate Fair Value Of Share-Based Award) (Details) (USD $)
12 Months Ended
Dec. 31, 2011
years
Dec. 31, 2010
years
Dec. 31, 2009
years
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected volatility 49.50% 50.30%  
Expected volatility, minimum     48.60%
Expected volatility, maximum     51.60%
Expected dividend yield 0.00% 0.00% 0.00%
Expected life (in years) 4.10 4.18  
Expected life (in years), minimum     4.18
Expected life (in years), maximum     4.47
Risk-free interest rate, minimum 0.67% 0.94% 1.62%
Risk-free interest rate, maximum 1.63% 1.91% 2.12%
Weighted-average fair value of stock options granted $ 8.36 $ 6.32 $ 5.79
Weighted-average fair value of restricted common stock granted     $ 15.43
Weighted-average fair value of restricted stock units granted $ 20.30 $ 15.30 $ 12.03
ANI Performance Award [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted-average fair value of restricted common stock granted $ 19.48 $ 16.91  
TSR Performance Award [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted-average fair value of restricted common stock granted $ 21.27 $ 17.62  
ANI And TSR Performance Award [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected volatility 49.50% 50.30%  
Expected dividend yield 0.00% 0.00%  
Expected life (in years) 4.10 4.18  
Risk-free interest rate 1.16% 1.33%