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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, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | $ 124,831 | $ 144,805 | $ 136,917
Cash and Cash Equivalents |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 16,641 | 23,696 |
Debt Instruments |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 91,778 | 36,245 |
Floating Rate Loan Fund |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 16,412 | 15,687 |
Large Cap U.S. Equity |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets |  | 20,208 |
Mid Cap U.S. Equity |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets |  | 13,597 |
Small Cap U.S. Equity |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets |  | 14,561 |
International Equity |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets |  | 20,811 |
Level 1 |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 43,140 | 108,560 |
Level 1 | Cash and Cash Equivalents |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 16,641 | 23,696 |
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 | 16,412 | 15,687 |
Level 1 | Large Cap U.S. Equity |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets |  | 20,208 |
Level 1 | Mid Cap U.S. Equity |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets |  | 13,597 |
Level 1 | Small Cap U.S. Equity |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets |  | 14,561 |
Level 1 | International Equity |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets |  | 20,811 |
Level 2 |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | 81,691 | 36,245 |
Level 2 | Debt Instruments |  |  |
Pension and other postretirement benefit plans |  |  |
Fair value of plan assets | $ 81,691 | $ 36,245 |
Level 2 | Corporate debt securities |  |  |
Pension and other postretirement benefit plans |  |  |
Percentage of investments in debt instruments | 80.00% | 81.00% |
Level 2 | Mortgage-backed instruments |  |  |
Pension and other postretirement benefit plans |  |  |
Percentage of investments in debt instruments | 4.00% | 10.00% |
Level 2 | Treasury instruments |  |  |
Pension and other postretirement benefit plans |  |  |
Percentage of investments in debt instruments |  | 7.00% |
Level 2 | Municipal debt securities |  |  |
Pension and other postretirement benefit plans |  |  |
Percentage of investments in debt instruments |  | 1.00% |
Level 2 | Asset-backed securities |  |  |
Pension and other postretirement benefit plans |  |  |
Percentage of investments in debt instruments | 16.00% |  |
Level 2 | Agency securities |  |  |
Pension and other postretirement benefit plans |  |  |
Percentage of investments in debt instruments |  | 1.00% |

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- Definition Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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