EMPLOYEE BENEFIT PLANS - Allocation of Defined Benefit Plan Assets (Details) - Qualified Plan - Qualified Pension Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
EMPLOYEE BENEFIT PLANS
Employer contributions	$ 18,800	$ 43,500
Target Allocation for 2017 of plan assets of defined benefit pension plan by category
Target allocation for 2017 (as a percent)	100.00%	100.00%
Allocation of plan assets of defined benefit pension plan by category
Total allocation (as a percent)	100.00%	100.00%
Cash and cash equivalents
Target Allocation for 2017 of plan assets of defined benefit pension plan by category
Target allocation for 2017 (as a percent)		2.00%
Allocation of plan assets of defined benefit pension plan by category
Total allocation (as a percent)		15.00%
Equity securities
Target Allocation for 2017 of plan assets of defined benefit pension plan by category
Target allocation for 2017 (as a percent)		60.00%
Allocation of plan assets of defined benefit pension plan by category
Total allocation (as a percent)		55.00%
Fixed income
Target Allocation for 2017 of plan assets of defined benefit pension plan by category
Target allocation for 2017 (as a percent)		38.00%
Allocation of plan assets of defined benefit pension plan by category
Total allocation (as a percent)		30.00%
Return-Seeking
Target Allocation for 2017 of plan assets of defined benefit pension plan by category
Target allocation for 2017 (as a percent)	60.00%
Allocation of plan assets of defined benefit pension plan by category
Total allocation (as a percent)	61.00%
Liability-Hedging Fixed Income
Target Allocation for 2017 of plan assets of defined benefit pension plan by category
Target allocation for 2017 (as a percent)	40.00%
Allocation of plan assets of defined benefit pension plan by category
Total allocation (as a percent)	39.00%