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Stock Compensation (Narrative) (Details) - USD ($)
shares in Thousands, $ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Employees purchased common stock, shares 36 45  
Capitalized stock compensation expense $ 106    
ESPP Options [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
ESPP, percentage of market price for eligible employees 85.00%    
RSAs, RSUs, And PSUs [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Authorized awards from approved stock incentive plans 273 239  
Aggregate grant date market value $ 5,900 $ 4,000  
Unrecognized compensation costs 10,400    
Stock Options [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Unrecognized compensation costs $ 3,100    
Expected weighted-average period for recognizing the unrecognized compensation costs, in years 2 years 1 month 6 days    
Restricted Stock Awards (RSAs) [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected weighted-average period for recognizing the unrecognized compensation costs, in years 1 year 6 months    
Restricted Stock Units (RSUs) [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected weighted-average period for recognizing the unrecognized compensation costs, in years 2 years 2 months 12 days    
Performance Stock Units (PSUs) [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percentage of target number of shares of common stock granted as Performance Stock Units     90.00%
Expected weighted-average period for recognizing the unrecognized compensation costs, in years 1 year 6 months    
Minimum [Member] | Performance Stock Units (PSUs) [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percentage of target number of shares of common stock granted as Performance Stock Units 60.00%   60.00%
Maximum [Member] | Performance Stock Units (PSUs) [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percentage of target number of shares of common stock granted as Performance Stock Units 150.00%   150.00%
Officers [Member] | Stock Options [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Grants of stock options 219 260