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

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- Definition

Amount of contribution received by defined benefit plan from employer which increases plan assets.

+ References

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Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

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Percentage of actual investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

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