Annual report pursuant to Section 13 and 15(d)

EMPLOYEE BENEFIT PLANS - Asset Allocation (Details)

v3.8.0.1
EMPLOYEE BENEFIT PLANS - Asset Allocation (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2018
Dec. 31, 2016
Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]        
Percentage of plan assets 100.00%   100.00%  
Percentage of investments for long-term growth, investment strategy mix 70.00%      
Percentage of investments for near-term benefit payments, investment strategy mix 30.00%      
Pension plan assets $ 219,905   $ 194,342 $ 190,640
Level 1        
Defined Benefit Plan Disclosure [Line Items]        
Pension plan assets 53,724   60,568  
Level 2        
Defined Benefit Plan Disclosure [Line Items]        
Pension plan assets 145,638   115,004  
Level 3        
Defined Benefit Plan Disclosure [Line Items]        
Pension plan assets $ 20,543   $ 18,770  
Cash and cash equivalents        
Defined Benefit Plan Disclosure [Line Items]        
Percentage of plan assets 2.40%   3.50%  
Pension plan assets $ 5,432   $ 6,834  
Cash and cash equivalents | Level 1        
Defined Benefit Plan Disclosure [Line Items]        
Pension plan assets $ 5,432   $ 6,834  
Common Stock        
Defined Benefit Plan Disclosure [Line Items]        
Percentage of plan assets 14.70%   20.70%  
Pension plan assets $ 32,049   $ 42,120  
Common Stock | Level 1        
Defined Benefit Plan Disclosure [Line Items]        
Pension plan assets $ 32,049   $ 42,120  
Domestic equity - all other        
Defined Benefit Plan Disclosure [Line Items]        
Percentage of plan assets 21.80%   21.70%  
Pension plan assets $ 48,511   $ 40,178  
Domestic equity - all other | Level 1        
Defined Benefit Plan Disclosure [Line Items]        
Pension plan assets 16,243   11,614  
Domestic equity - all other | Level 2        
Defined Benefit Plan Disclosure [Line Items]        
Pension plan assets $ 32,268   $ 28,564  
International equity        
Defined Benefit Plan Disclosure [Line Items]        
Percentage of plan assets 16.40%   21.00%  
Pension plan assets $ 36,156   $ 40,767  
International equity | Level 1        
Defined Benefit Plan Disclosure [Line Items]        
Pension plan assets     0  
International equity | Level 2        
Defined Benefit Plan Disclosure [Line Items]        
Pension plan assets $ 36,156   $ 40,767  
Debt securities - core fixed income        
Defined Benefit Plan Disclosure [Line Items]        
Percentage of plan assets 35.20%   23.50%  
Pension plan assets $ 77,214   $ 45,673  
Debt securities - core fixed income | Level 1        
Defined Benefit Plan Disclosure [Line Items]        
Pension plan assets      
Debt securities - core fixed income | Level 2        
Defined Benefit Plan Disclosure [Line Items]        
Pension plan assets $ 77,214   $ 45,673  
Real estate        
Defined Benefit Plan Disclosure [Line Items]        
Percentage of plan assets 6.50%   6.40%  
Pension plan assets $ 14,074   $ 12,527  
Real estate | Level 3        
Defined Benefit Plan Disclosure [Line Items]        
Pension plan assets $ 14,074   $ 12,527  
Alternative/Opportunistic/Special        
Defined Benefit Plan Disclosure [Line Items]        
Percentage of plan assets 3.00%   3.20%  
Pension plan assets $ 6,469   $ 6,243  
Alternative/Opportunistic/Special | Level 3        
Defined Benefit Plan Disclosure [Line Items]        
Pension plan assets $ 6,469   $ 6,243  
Scenario, Forecast        
Defined Benefit Plan Disclosure [Line Items]        
Target allocation      
Scenario, Forecast | Cash and cash equivalents | Minimum        
Defined Benefit Plan Disclosure [Line Items]        
Target allocation   0.00%    
Scenario, Forecast | Cash and cash equivalents | Maximum        
Defined Benefit Plan Disclosure [Line Items]        
Target allocation   5.00%    
Scenario, Forecast | Common Stock | Minimum        
Defined Benefit Plan Disclosure [Line Items]        
Target allocation   0.00%    
Scenario, Forecast | Common Stock | Maximum        
Defined Benefit Plan Disclosure [Line Items]        
Target allocation   40.00%    
Scenario, Forecast | Domestic equity - all other | Minimum        
Defined Benefit Plan Disclosure [Line Items]        
Target allocation   0.00%    
Scenario, Forecast | Domestic equity - all other | Maximum        
Defined Benefit Plan Disclosure [Line Items]        
Target allocation   40.00%    
Scenario, Forecast | International equity | Minimum        
Defined Benefit Plan Disclosure [Line Items]        
Target allocation   0.00%    
Scenario, Forecast | International equity | Maximum        
Defined Benefit Plan Disclosure [Line Items]        
Target allocation   30.00%    
Scenario, Forecast | Debt securities - core fixed income | Minimum        
Defined Benefit Plan Disclosure [Line Items]        
Target allocation   15.00%    
Scenario, Forecast | Debt securities - core fixed income | Maximum        
Defined Benefit Plan Disclosure [Line Items]        
Target allocation   50.00%    
Scenario, Forecast | Real estate | Minimum        
Defined Benefit Plan Disclosure [Line Items]        
Target allocation   0.00%    
Scenario, Forecast | Real estate | Maximum        
Defined Benefit Plan Disclosure [Line Items]        
Target allocation   20.00%    
Scenario, Forecast | Alternative/Opportunistic/Special | Minimum        
Defined Benefit Plan Disclosure [Line Items]        
Target allocation   0.00%    
Scenario, Forecast | Alternative/Opportunistic/Special | Maximum        
Defined Benefit Plan Disclosure [Line Items]        
Target allocation   20.00%