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Stock-Based Compensation (Restricted Stock Award Activity) (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Restricted Stock      
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Unvested at beginning of period (in shares) 1,310,019    
Granted (in shares) 1,590,662    
Cancelled (in shares) (470,626)    
Vested (in shares) (293,612)    
Unvested at end of period (in shares) 2,136,443 1,310,019  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]      
Unvested, Weighted Average Fair Value per Share at Grant Date, beginning balance (in USD per share) $ 10.19    
Granted, Weighted Average Fair Value Per Share at Grant Date (in USD per share) 5.01 $ 8.29 $ 16.03
Forfeited, Weighted Average Fair Value Per Share at Grant Date (in USD per share) 9.74    
Vested, Weighted Average Fair Value Per Share at Grant Date (in USD per share) 11.39    
Unvested, Weighted Average Fair Value per Share at Grant Date, ending balance (in USD per share) $ 6.27 $ 10.19  
Granted, Grant Date Fair Value $ 7,969    
Vested, Vest Date Fair Value $ 1,757    
Performance stock units      
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Granted (in shares) [1] 513,011    
[1] Shares granted in 2017 include 513,011 performance stock units that have certain performance conditions required to be achieved to vest.