EMPLOYEE BENEFITS (Obligation and Funded Status) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits
Reconciliation of benefit obligation
Benefit obligation at beginning of year	$ 252,374	$ 202,156
Service cost	10,829	7,989	$ 8,701
Interest cost	8,266	8,320	7,500
Actuarial loss (gain)	38,920	39,598
Adjustment for plan amendment	(32,175)	0
Benefit payments	(6,470)	(5,689)
Benefit obligation at end of year	271,744	252,374	202,156
Reconciliation of fair value of plan assets
Fair value of plan assets at beginning of year	199,466	164,819
Actual return on plan assets	45,739	36,336
Employer contributions	10,000	4,000
Benefit payments	(6,470)	(5,689)
Fair value of plan assets at end of year	248,735	199,466	164,819
Funded status at end of year	(23,009)	(52,908)
Accumulated pension benefit obligation	271,515	226,196
Post-retirement Benefits
Reconciliation of benefit obligation
Benefit obligation at beginning of year	31,001	30,973
Service cost	1,728	1,823	2,998
Interest cost	1,014	1,274	2,009
Actuarial loss (gain)	(1,084)	(1,806)
Adjustment for plan amendment	0	0
Benefit payments	(993)	(1,263)
Benefit obligation at end of year	31,666	31,001	30,973
Reconciliation of fair value of plan assets
Fair value of plan assets at beginning of year	0	0
Actual return on plan assets	0	0
Employer contributions	993	1,263
Benefit payments	(993)	(1,263)
Fair value of plan assets at end of year	0	0	$ 0
Funded status at end of year	$ (31,666)	$ (31,001)