EMPLOYEE BENEFIT PLANS - Allocation of Defined Benefit Plan Assets (Details) - Qualified Plan - Qualified Pension Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
EMPLOYEE BENEFIT PLANS
Employer contributions	$ 17,400	$ 18,800
Defined Benefit Plan, Plan Assets, Allocations [Abstract]
Target allocation (as a percent)	100.00%
Allocation of plan assets of defined benefit pension plan by category
Total allocation (as a percent)	100.00%	100.00%
Return-Seeking
Defined Benefit Plan, Plan Assets, Allocations [Abstract]
Target allocation (as a percent)	60.00%
Allocation of plan assets of defined benefit pension plan by category
Total allocation (as a percent)	61.00%	61.00%
Liability-Hedging Fixed Income
Defined Benefit Plan, Plan Assets, Allocations [Abstract]
Target allocation (as a percent)	40.00%
Allocation of plan assets of defined benefit pension plan by category
Total allocation (as a percent)	39.00%	39.00%