POSTRETIREMENT BENEFITS (net periodic benefit income and actuarial assumptions) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net periodic benefit income
Interest cost	$ 2,727	$ 2,626	$ 2,896
Expected return on plan assets	(6,957)	(7,737)	(7,128)
Amortization of prior service credit	(1,421)	(1,421)	(1,421)
Amortization of net actuarial losses	3,223	2,884	3,637
Net periodic benefit income	$ (2,428)	$ (3,648)	$ (2,016)
Participants under age 65 [Member]
Health care cost trend rates
Health care cost trend rate assumed for next year	7.40%	7.70%	7.90%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate)	4.50%	4.50%	4.50%
Year that the rate reaches the ultimate trend rate	2029	2029	2025
Participants age 65 and older [Member]
Health care cost trend rates
Health care cost trend rate assumed for next year	8.40%	8.70%	9.10%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate)	4.50%	4.50%	4.50%
Year that the rate reaches the ultimate trend rate	2029	2029	2025
Postretirement benefit plan [Member]
Net periodic benefit income
Interest cost	$ 2,617	$ 2,529
Actuarial assumptions
Discount rate, benefit obligation	3.03%	4.13%
Discount rate, net periodic benefit income	4.13%	3.46%	3.81%
Expected return on plan assets	6.25%	6.25%	6.25%
Pension plan [Member]
Net periodic benefit income
Interest cost	$ 111	$ 97
Actuarial assumptions
Discount rate, benefit obligation	2.76%	4.01%
Discount rate, net periodic benefit income	4.01%	3.35%	3.66%