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Stockholders' Equity (Details 1) - USD ($)
$ / shares in Units, $ in Millions
 3 Months Ended 12 Months Ended 252 Months Ended
Mar. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2017
Aug. 31, 2014
Stock repurchase program            
Dividends paid (in dollars per share)   $ 0 $ 0.85 $ 3.4    
Common Stock            
Stock repurchase program            
Dividends paid (in dollars per share) $ 0.85          
Stock repurchased under current and previously announced share repurchase programs         $ 1,200.0  
Stock repurchased under current and previously announced share repurchase programs (in shares)         6,800,000  
Common Stock | 2012 Stock Repurchase program            
Stock repurchase program            
Common stock repurchased (in shares)   0        
Authorized amount to repurchase shares           $ 20.0
Remaining amount available to repurchase shares   $ 11.4     $ 11.4  
Common stock received in lieu of cash from stock option exercises and vesting of non-vested shares (in shares)   9,310        
Common stock received in lieu of cash from stock option exercises and vesting of non-vested shares   $ 0.1