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EMPLOYEE BENEFIT PLANS (Nonunion Plan Assets - FV) (Details) - Nonunion Defined Benefit Pension Plan - USD ($) $ in Thousands | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | --- | ---
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | $ 26,646 | $ 124,831 | $ 144,805
Cash and Cash Equivalents |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 19,856 | 16,641 |
Debt Instruments |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 10 | 91,778 |
Floating Rate Loan Fund |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 6,780 | 16,412 |
Level 1 |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 26,636 | 43,140 |
Level 1 | Cash and Cash Equivalents |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 19,856 | 16,641 |
Level 1 | Debt Instruments |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets |  | 10,087 |
Level 1 | Floating Rate Loan Fund |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 6,780 | 16,412 |
Level 2 |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 10 | 81,691 |
Level 2 | Debt Instruments |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | $ 10 | $ 81,691 |
Level 2 | Corporate debt securities |  |  |
Pension and other postretirement benefit plans |  |  |
Percentage of investments in debt instruments |  | 80.00% |
Level 2 | Asset-backed securities |  |  |
Pension and other postretirement benefit plans |  |  |
Percentage of investments in debt instruments |  | 16.00% |
Level 2 | Mortgage-backed instruments |  |  |
Pension and other postretirement benefit plans |  |  |
Percentage of investments in debt instruments |  | 4.00% |

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