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Stockholders' Equity (Narrative) (Details) - $ / shares
3 Months Ended 22 Months Ended
Mar. 27, 2014
Mar. 31, 2018
Dec. 31, 2017
Mar. 31, 2016
Class of Stock [Line Items]        
Common stock, shares authorized (in shares)   100,000,000 100,000,000  
Common stock, par value (in dollars per share)   $ 0.01 $ 0.01  
Common stock, shares issued (in shares)   50,685,699 50,598,901  
Common stock, shares outstanding (in shares)   50,685,699 50,598,901  
Preferred stock, shares authorized (in shares)   5,000,000 5,000,000  
Preferred stock, par value (in dollars per share)   $ 0.01 $ 0.01  
Preferred stock, shares issued (in shares)   0 0  
Preferred stock, shares outstanding (in shares)   0 0  
Number of shares authorized to be repurchased (in shares)       1,000,000
Number of shares repurchased (in shares)     0  
Common Stock | Challenger Subsidiary        
Class of Stock [Line Items]        
Common stock issued in connection with the investment in the Challenger Subsidiary (in shares)   20,000    
Preferred Share Purchase Right        
Class of Stock [Line Items]        
Preferred stock, par value (in dollars per share) $ 0.01      
Preferred share purchase right dividend (in shares) 1      
Exercise price of rights (in dollars per share) $ 30.00      
Series B Junior Participating Preferred Stock        
Class of Stock [Line Items]        
Number of securities called by each right (in shares) 0.001      
Preferred Stock        
Class of Stock [Line Items]        
Number of securities called by each right (in shares) 0.001