Common Stock (Schedule of Restricted Stock Unit Activity) (Details) (Restricted Stock Units (RSUs), USD $)
In Thousands, except Per Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Restricted Stock Units (RSUs)
     
Stock Units      
Nonvested as of December 31, 2013 (in shares) 763    
Granted (in shares) 805 894 1,216
Vested (in shares) (817)    
Forfeited (in shares) (49)    
Nonvested as of December 31, 2014 (in shares) 702 763  
Weighted-Average Grant Date Fair Value      
Nonvested as of December 31, 2013 (in dollars per share) $ 46.06    
Granted (in dollars per share) $ 92.28 $ 57.50 $ 43.98
Vested (in dollars per share) $ 71.16    
Forfeited (in dollars per share) $ 63.22    
Nonvested as of December 31, 2014 (in dollars per share) $ 68.11 $ 46.06