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Share-Based Compensation - MSUs Activity (Details) - MSUs - $ / shares
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Weighted Number of Shares      
Nonvested at beginning of period (in shares) 511,000    
Granted (in shares) 474,000    
Vested (in shares) (155,595)    
Forfeited (in shares) (86,000)    
Nonvested at end of period (in shares) 743,000 511,000  
Weighted Average Grant Date Fair Value      
Nonvested at January 1 (in dollars per share) $ 38.43    
Granted (in dollars per share) 30.06 $ 40.20 $ 34.55
Vested (in dollars per share) 34.80    
Forfeited (in dollars per share) 34.34    
Nonvested at December 31 (in dollars per share) $ 34.33 $ 38.43