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DEFERRED COMPENSATION PLANS - Narrative (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]      
Cash surrender value of life insurance $ 79,600 $ 78,100  
Deferred compensation arrangement with individual, recorded liability 874 944  
Deferred compensation arrangement with individual, compensation expense 1,416 1,127 $ 849
Supplemental Employee Retirement Plan      
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]      
Deferred compensation arrangement with individual, recorded liability $ 4,962 $ 3,570