Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation Plans (Details)

v3.8.0.1
Stock-Based Compensation Plans (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Mar. 01, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Mar. 01, 2016
May 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Shares available for issuance (in shares)   436,532        
Stock-based compensation   $ 3,068 $ 2,109 $ 2,081    
Tax withholding associated with awards issued   500 499 342    
Compensation expense not yet recognized   $ 2,300 $ 1,100      
Weighted average amortization period of compensation not yet recognized   1 year 8 months 24 days 1 year 10 months 24 days      
Restricted Stock            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Stock-based compensation   $ 3,058 $ 2,099 2,040    
Stock-based compensation included in costs and operating expenses   3,068 2,109 2,081    
Income tax benefit recognized for stock-based compensation   (1,180) (811) (800)    
Stock-based compensation expense, net of income tax benefit   1,888 1,298 1,281    
Restricted Stock | Non-employee Directors            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Stock-based compensation   642 544 617    
Restricted Stock | Employee            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Stock-based compensation   $ 2,416 $ 1,555 $ 1,423    
Restricted Stock Plan 2006            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Shares authorized (in shares)     1,000,000     500,000
Restricted Stock Plan 2006 | Non-employee Directors            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Restricted stock awarded (in shares)   16,100 17,600 18,000    
Stock-based compensation   $ 642 $ 544 $ 617    
Restricted Stock Plan 2006 | Employee            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Restricted stock awarded (in shares) 23,508          
Grant date fair value (in dollars per share) $ 40.14          
Vested award is paid in our shares 100.00%       100.00%  
Vesting period   3 years        
Restricted Stock Plan 2006 | Restricted Stock            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Grant date fair value (in dollars per share)   $ 39.85 $ 30.89 $ 34.29