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Stockholders' Equity Stockholders' Equity (Summary of unvested restricted stock awards) (Details) - $ / shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Restricted Stock Units (RSUs)      
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Awards (in shares) 86,260 27,250 16,900
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 year (in shares) 54,000    
Awards (in shares) 86,000    
Vestings (in shares) (32,000)    
Cancellations (in shares) (20,000)    
Unvested at end of year (in shares) 89,000 54,000  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]      
Unvested at beginning of year ( in usd per share) $ 24.09    
Awards ( in usd per share) 25.18    
Vestings ( in usd per share) 22.68    
Cancellations ( in usd per share) 25.41    
Unvested at beginning of year ( in usd per share) $ 25.38 $ 24.09