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Stock-Based Compensation (Details 2) (USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Weighted Average Grant Date Fair Value per Unit      
Stock based compensation expense $ 33,500,000 $ 39,500,000 $ 14,400,000
Restricted Stock Units
     
Summary of restricted stock award activity      
Outstanding at the beginning of the period (in shares) 343,654    
Granted and fully vested (in shares) 38,304 59,402 53,922
Issued (in shares) (124,224)    
Outstanding at the end of the period (in shares) 257,734 343,654  
Weighted Average Grant Date Fair Value per Unit      
Outstanding at the beginning of the period (in dollars per share) $ 15.75    
Granted (in dollars per share) $ 36.55 $ 20.88 $ 20.04
Issued (in dollars per share) $ 17.11    
Outstanding at the end of the period (in dollars per share) $ 18.19 $ 15.75  
Aggregate Intrinsic Value 12,820,000    
Stock based compensation expense $ 1,400,000 $ 1,200,000 $ 1,100,000