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BENEFIT PLANS, 401(K) Employee Stock Ownership Plan (Details) - 401(k) Employee Stock Ownership Plan [Member] - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Defined Contribution Plan Disclosure [Line Items] |  |  |
Percentage of first eligible compensation fully matched by employer | 3.00% |  |
Percentage of matching contribution in the form of common stock | 100.00% |  |
Percentage of the next eligible compensation matched at 50% by employer | 3.00% |  |
Percentage of matching contributions for the next eligible compensation in the form of company stock | 50.00% |  |
(Income)/expense recognized under plan | $ 5.3 | $ 4.3 | $ 3.6
Interest credit contribution expense recognized for 401(k) plan | $ 0.8 | $ 0.7 | $ 1.1
Minimum [Member] |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Contribution from eligible compensation | 1.00% |  |
Maximum [Member] |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Contribution from eligible compensation | 90.00% |  |

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