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EMPLOYEE BENEFIT PLANS - Components of net periodic benefit cost (Details) - Retirement Income Plan - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]      
Service cost for benefits earned during the period $ 0 $ 0 $ 0
Interest cost on projected benefit obligation 266 274 259
Expected return on plan assets (415) (406) (421)
Amortization of net loss 91 84 76
Net periodic benefit, Total $ (58) $ (48) $ (86)