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EMPLOYEE BENEFIT PLANS (Nonunion Plan Assets - FV) (Details) - Nonunion Defined Benefit Pension Plan - USD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | $ 144,805 | $ 136,917 | $ 158,265
Cash and Cash Equivalents |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 23,696 | 19,079 |
Debt Instruments |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 36,245 | 26,662 |
Floating Rate Loan Fund |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 15,687 | 15,868 |
Large Cap U.S. Equity |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 20,208 | 23,459 |
Mid Cap U.S. Equity |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 13,597 | 14,276 |
Small Cap U.S. Equity |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 14,561 | 14,135 |
International Equity |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 20,811 | 23,438 |
Level 1 |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 108,560 | 110,255 |
Level 1 | Cash and Cash Equivalents |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 23,696 | 19,079 |
Level 1 | Floating Rate Loan Fund |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 15,687 | 15,868 |
Level 1 | Large Cap U.S. Equity |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 20,208 | 23,459 |
Level 1 | Mid Cap U.S. Equity |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 13,597 | 14,276 |
Level 1 | Small Cap U.S. Equity |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 14,561 | 14,135 |
Level 1 | International Equity |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 20,811 | 23,438 |
Level 2 |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 36,245 | 26,662 |
Level 2 | Debt Instruments |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | $ 36,245 | $ 26,662 |
Level 2 | Corporate debt securities |  |  |
Pension and other postretirement benefit plans |  |  |
Percentage of investments in debt instruments | 81.00% | 74.00% |
Level 2 | Mortgage-backed instruments |  |  |
Pension and other postretirement benefit plans |  |  |
Percentage of investments in debt instruments | 10.00% | 17.00% |
Level 2 | Treasury instruments |  |  |
Pension and other postretirement benefit plans |  |  |
Percentage of investments in debt instruments | 7.00% | 6.00% |
Level 2 | Municipal debt securities |  |  |
Pension and other postretirement benefit plans |  |  |
Percentage of investments in debt instruments | 1.00% | 2.00% |
Level 2 | Agency securities |  |  |
Pension and other postretirement benefit plans |  |  |
Percentage of investments in debt instruments | 1.00% | 1.00% |

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