EMPLOYEE BENEFIT PLANS - Postretirement (Details) - Postretirement benefit plans - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Postretirement benefit plan disclosure
Assumed ultimate health care cost trend rate (as a percent)	3.00%
Accumulated benefit obligation after plan amendment	$ 13,743	$ 12,451
Amounts recognized in accumulated other comprehensive loss (pre-tax)
Prior service credit	(3,066)
Net actuarial gain	(808)
Net amount recognized in accumulated other comprehensive loss	(3,874)
Estimated amount to be amortized from accumulated other comprehensive loss (gain) into net periodic benefit cost during next fiscal year
Actuarial gain	123
Prior service credit	(1,227)
Changes in the accumulated postretirement benefit obligation
Benefit obligation, beginning of the period	12,451	13,497
Service cost	270	337	$ 323
Interest cost	499	455	468
Actuarial (gain)/loss	922	(1,409)
Benefits paid	(399)	(429)
Benefit obligation, end of the period	13,743	12,451	13,497
Net periodic postretirement benefit cost
Service cost-benefits attributed to service during the period	270	337	323
Interest cost on the accumulated postretirement benefit obligation	499	455	468
Net amortization	(1,522)	(1,324)	(1,462)
Net periodic postretirement benefit cost (income)	$ (753)	$ (532)	$ (671)