BENEFIT PLANS (Combined Funded Status of Plans and their Reconciliation with Related Amounts Recognized in Consolidated Financial Statements - Postretirement Benefits) (Details) - Other Postretirement Benefit Plans, Defined Benefit [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in Benefit Obligation
Projected benefit obligation at beginning of year	$ 41,187	$ 40,834
Service cost	1,520	1,317	$ 1,358
Interest cost	969	1,388	1,240
Actuarial loss	(5,111)	2,677
Benefits paid	(4,682)	(5,029)	(6,099)
Projected benefit obligation at end of year	33,883	41,187	40,834
Change in Fair Value of Plan Assets
Fair value of assets at beginning of year	0	0
Actual return on plan assets	0	0
Fair value of assets at end of year	0	0	$ 0
Funded status	(33,883)	(41,187)
Amounts Recognized in the Consolidated Balance Sheets
Current liabilities	(4,471)	(5,339)
Noncurrent liabilities	(29,412)	(35,848)
Net amount recognized	(33,883)	(41,187)
Amounts Recognized in Accumulated Other Comprehensive Income
Net actuarial gain	(19,003)	(14,642)
Prior service credit	(3,656)	(7,575)
Total amount recognized	$ (22,659)	$ (22,217)