EMPLOYEE BENEFIT PLANS - Postretirement (Details) - Postretirement benefit plans - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Postretirement benefit plan disclosure
Assumed ultimate health care cost trend rate (as a percent)	3.00%
Accumulated benefit obligation after plan amendment	$ 12,451	$ 13,497
Amounts recognized in accumulated other comprehensive loss (pre-tax)
Prior service credit	(4,293)
Net actuarial gain	(2,025)
Net amount recognized in accumulated other comprehensive loss	(6,318)
Estimated amount to be amortized from accumulated other comprehensive loss (gain) into net periodic benefit cost during next fiscal year
Actuarial gain	295
Prior service credit	(1,227)
Changes in the accumulated postretirement benefit obligation
Benefit obligation, beginning of the period	13,497	12,128
Service cost	337	323	$ 331
Interest cost	455	468	462
Actuarial (gain)/loss	(1,409)	897
Benefits paid	(429)	(319)
Benefit obligation, end of the period	12,451	13,497	12,128
Net periodic postretirement benefit cost
Service cost benefits attributed to service during the period	337	323	331
Interest cost on the accumulated postretirement benefit obligation	455	468	462
Net amortization	(1,324)	(1,462)	(1,642)
Net periodic postretirement benefit cost (income)	$ (532)	$ (671)	$ (849)