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EMPLOYEE BENEFIT PLANS EMPLOYEE BENEFIT PLANS - Employee benefit plan amounts recognized in the Consolidated Balance Sheets and Consolidated Statements of Income (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Retirement Benefits [Abstract]        
Service cost $ 1,736 $ 1,238 $ 4,766 $ 3,715
Interest cost 601 589 1,792 1,767
Expected return on plan assets (2,450) (2,481) (7,360) (7,443)
Amortization of prior service cost (104) (103) (310) (310)
Defined Benefit Plan, Amortization of Gain (Loss) 556 438 1,633 1,315
Net periodic benefit cost (income) $ 339 $ (319) $ 521 $ (956)