RETIREMENT PLANS (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Components of net periodic benefit cost [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%
Pension Benefits [Member]
Components of net periodic benefit cost [Abstract]
Service cost	$ 1,742	$ 3,351	$ 8,934	$ 10,053
Interest cost	3,320	3,531	10,409	10,594
Expected return on plan assets	(4,595)	(4,202)	(13,600)	(12,606)
Amortization of actuarial (gain) loss	981	1,372	3,419	4,115
Net periodic benefit cost	1,448	4,052	9,162	12,156
SERP [Member]
Components of net periodic benefit cost [Abstract]
Service cost	0	0	0	0
Interest cost	14	16	43	49
Expected return on plan assets	0	0	0	0
Amortization of actuarial (gain) loss	7	7	21	20
Net periodic benefit cost	21	23	64	69
Other Postretirement Benefits [Member]
Components of net periodic benefit cost [Abstract]
Service cost	0	0	0	0
Interest cost	6	7	20	22
Amortization of actuarial (gain) loss	(166)	(186)	(501)	(560)
Net periodic benefit cost	$ (160)	$ (179)	$ (481)	$ (538)