EMPLOYEE BENEFIT PLANS - Postretirement (Details) - Postretirement benefit plans - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Postretirement benefit plan disclosure
Assumed ultimate health care cost trend rate (as a percent)	3.00%
Accumulated benefit obligation after plan amendment	$ 13,487	$ 13,743
Amounts recognized in accumulated other comprehensive loss (pre-tax)
Prior service credit	(1,840)
Net actuarial gain	(1,196)
Net amount recognized in accumulated other comprehensive loss	(3,036)
Changes in the accumulated postretirement benefit obligation
Benefit obligation, beginning of the period	13,743	12,451
Service cost	288	270	$ 337
Interest cost	403	499	455
Actuarial (gain)/loss	(510)	922
Benefits paid	(437)	(399)
Benefit obligation, end of the period	13,487	13,743	12,451
Net periodic postretirement benefit cost
Service cost-benefits attributed to service during the period	288	270	337
Interest cost on the accumulated postretirement benefit obligation	403	499	455
Net amortization	(1,349)	(1,522)	(1,324)
Net periodic postretirement benefit cost (income)	$ (658)	$ (753)	$ (532)

For defined benefit pension plans, the actuarial present value, after plan amendment, of benefits (whether vested or nonvested) attributed by the pension benefit formula to employee service rendered before a specified date and based on employee service and compensation (if applicable) before that date. The accumulated benefit obligation differs from the projected benefit obligation in that it includes no assumption about future compensation levels. For plans with flat-benefit or nonpay-related pension benefit formulas, the accumulated benefit obligation and the projected benefit obligation are the same.

No definition available.