EMPLOYEE BENEFIT PLANS - ABO and PBO (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Summary of pension obligations greater than fair value of related plan assets
Total accumulated benefit obligations	$ 2,506,726	$ 2,301,948
Plans with pension obligations in excess of plan assets:
PBO	1,950,552	1,841,479
ABO	1,948,544	1,819,838
Fair value of plan assets	1,681,598	1,423,787
United States
Summary of pension obligations greater than fair value of related plan assets
Total accumulated benefit obligations	1,940,549	1,812,813
Plans with pension obligations in excess of plan assets:
PBO	1,940,704	1,832,786
ABO	1,940,549	1,812,813
Fair value of plan assets	1,681,598	1,423,787
Foreign
Summary of pension obligations greater than fair value of related plan assets
Total accumulated benefit obligations	566,177	489,135
Plans with pension obligations in excess of plan assets:
PBO	9,848	8,693
ABO	7,995	7,025
Fair value of plan assets	$ 0	$ 0

Schedule of pension obligations in excess of fair value of plan assets.

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Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level.

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Amount of accumulated benefit obligation for defined benefit plan with accumulated benefit obligation in excess of plan assets.

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Amount of plan asset for defined benefit plan with accumulated benefit obligation in excess of plan assets.

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Amount of projected benefit obligation for defined benefit pension plan with accumulated benefit obligation in excess of plan assets.

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