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Stock-based Compensation (Narrative) (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Aug. 12, 2009
Stock based Compensation        
Number of options outstanding (in shares) 291,775 529,720    
Number of options exercisable (in shares) 291,775 529,720    
Options outstanding, weighted average exercise price (in dollars per share) $ 9.26 $ 9.09    
Options exercisable, weighted average exercise price (in dollars per share) $ 9.26 $ 9.09    
Weighted average remaining contractual term for all options outstanding 1 year 9 months 18 days      
Weighted average remaining contractual term for all exercisable options 1 year 9 months 18 days      
Exercise of stock options (in shares) 226,845 202,000 183,000  
Exercise of stock options, weighted average exercise price (in dollars per share) $ 8.89      
Stock options canceled (in shares) 11,100      
Stock options canceled, weighted average exercise price (in dollars per share) $ 8.51      
Total intrinsic value of options exercised (in dollars) $ 1.6 $ 0.8 $ 1.0  
Aggregate intrinsic value of options outstanding (in dollars) 2.4      
Aggregate intrinsic value of options exercisable (in dollars) $ 2.4      
Restricted stock awards        
Stock based Compensation        
Weighted average grant date fair value of granted shares (in dollars per share) $ 15.84 $ 11.57 $ 13.94  
Weighted average grant date fair value of vested shares $ 17.1 $ 8.4 $ 9.0  
2016 Equity Incentive Plan | Restricted stock and stock option        
Stock based Compensation        
Number of shares authorized (in shares) 7,529,200      
Number of shares authorized, remaining (in shares) 4,505,801      
Director Plan | Employee stock option        
Stock based Compensation        
Number of shares authorized (in shares)       75,000
Director Plan | Restricted stock awards        
Stock based Compensation        
Number of shares authorized (in shares)       150,000