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RETIREMENT PLANS (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2018
Mar. 31, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Retirement Plans [Abstract]          
Service period of participants not impacted by pension plan amendment       15 years  
Age of plan participants not impacted by pension plan amendment       50 years  
Service period of participants who are age fifty not impacted by pension plan amendment       10 years  
Decrease in pension plan projected benefit obligation       $ (33,433)  
Pension plan defined benefit plan cost increase limit percentage       4.00%  
Higman [Member]          
Retirement Plans [Abstract]          
Decrease in pension plan projected benefit obligation       $ (3,692)  
Pension contributions   $ 6,717      
Expected additional contribution $ 1,385     1,385  
Pension Plan [Member]          
Components of net periodic benefit cost [Abstract]          
Service cost 1,722   $ 1,742 5,816 $ 8,934
Interest cost 3,939   3,320 11,544 10,409
Expected return on plan assets (5,696)   (4,595) (16,712) (13,600)
Amortization of actuarial loss 723   981 2,168 3,419
Net periodic benefit cost 688   1,448 2,816 9,162
SERP [Member]          
Components of net periodic benefit cost [Abstract]          
Service cost 0   0 0 0
Interest cost 12   14 36 43
Expected return on plan assets 0   0 0 0
Amortization of actuarial loss 6   7 18 21
Net periodic benefit cost 18   21 54 64
Other Postretirement Benefits [Member]          
Components of net periodic benefit cost [Abstract]          
Service cost 0   0 0 0
Interest cost 6   6 18 20
Amortization of actuarial loss (149)   (166) (447) (501)
Net periodic benefit cost $ (143)   $ (160) $ (429) $ (481)