Annual report pursuant to Section 13 and 15(d)

Equity Compensation - Narrative (Details)

v3.10.0.1
Equity Compensation - Narrative (Details) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award        
Period of options granted (in years) 5 years      
Stock Compensation Expense $ 3,098,000 $ 2,598,000 $ 2,281,000  
Stock Option        
Share-based Compensation Arrangement by Share-based Payment Award        
Share price (in usd per share) $ 30.45 $ 36.06 $ 29.43  
Weighted average fair value of options vested (in usd per share) $ 16.54 $ 12.39 $ 10.48  
Total fair value of options that vested during the year $ 1,400,000 $ 1,600,000 $ 1,400,000  
Total compensation costs related to non-vested awards $ 4,900,000      
Weighted average period (in years) 2 years 3 months 7 days      
Options outstanding (in shares) 1,327,919 1,506,604 1,539,017 1,661,700
Weighted average fair value of options granted (in usd per share) $ 14.64 $ 15.30 $ 14.65  
Restricted Stock Units (RSUs)        
Share-based Compensation Arrangement by Share-based Payment Award        
Period of options granted (in years) 3 years      
Number of awards granted in period (in shares) 43,930      
Weighted-average price of awards (in usd per share) $ 34.11      
Number of awards vested in period (in shares) 0      
Stock Compensation Expense $ 400,000      
Total compensation costs related to non-vested awards $ 1,100,000      
Weighted average period (in years) 2 years      
Employee Stock        
Share-based Compensation Arrangement by Share-based Payment Award        
Share price (in usd per share) $ 32.13      
Cash compensation limit $ 21,250      
Common stock price to market value (percentage) 85.00%      
Number of shares employees had subscribed to purchase (in shares) 127,344      
Weighted average fair value of options granted (in usd per share) $ 8.48 $ 5.15 $ 8.59  
Stock Incentive Plan        
Share-based Compensation Arrangement by Share-based Payment Award        
Stock option exercisable period (not exceeding, in years) 10 years      
Period of options granted (in years) 5 years      
Options outstanding (in shares) 931,193      
Directors Stock Option Plan        
Share-based Compensation Arrangement by Share-based Payment Award        
Stock option exercisable period (not exceeding, in years) 10 years      
Period of options granted (in years) 6 months      
Options outstanding (in shares) 199,245      
Long Term Incentive Plan        
Share-based Compensation Arrangement by Share-based Payment Award        
Options outstanding (in shares) 240,500      
Options available for future grant (in shares) 1,518,848      
Director        
Share-based Compensation Arrangement by Share-based Payment Award        
Period of options granted (in years) 6 months      
Key Employee        
Share-based Compensation Arrangement by Share-based Payment Award        
Period of options granted (in years) 5 years      
Maximum        
Share-based Compensation Arrangement by Share-based Payment Award        
Stock option exercisable period (not exceeding, in years) 10 years