Annual report pursuant to Section 13 and 15(d)

Employee Retirement Plans - Fair Value (Details)

v3.8.0.1
Employee Retirement Plans - Fair Value (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Employee retirement plans        
Total pension plan assets $ 33,903 $ 29,223    
Level 2        
Employee retirement plans        
Total pension plan assets 31,877 27,475    
Level 3        
Employee retirement plans        
Total pension plan assets 2,026 1,748 $ 1,748 $ 1,364
Equity holdings        
Employee retirement plans        
Total pension plan assets 13,384 15,654    
Equity holdings | Level 2        
Employee retirement plans        
Total pension plan assets 13,384 15,654    
Fixed-income holdings        
Employee retirement plans        
Total pension plan assets 18,493 11,821    
Fixed-income holdings | Level 2        
Employee retirement plans        
Total pension plan assets 18,493 11,821    
Alternative investments        
Employee retirement plans        
Total pension plan assets 2,026 1,748    
Alternative investments | Level 3        
Employee retirement plans        
Total pension plan assets 2,026 1,748    
Pension plan        
Employee retirement plans        
Total pension plan assets $ 33,903 $ 29,223 $ 26,378