Stockholders' Equity (Details) (Treasury Stock, USD $)
In Millions, except Share data, unless otherwise specified
0 Months Ended 3 Months Ended
Mar. 31, 2015
Mar. 31, 2015
Dec. 31, 2014
Treasury Stock
     
Equity, Class of Treasury Stock [Line Items]      
Amount of shares authorized to be repurchased     $ 205.0
Shares repurchased 3,736,449 1,009,700  
Cost of shares repurchased $ 106.2 $ 31.1  
Average purchase price $ 28.41 $ 30.79