RETIREMENT PLANS - Rate Assumptions (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
One-percentage change in assumed health care cost trend rates
Accumulated postretirement benefit obligation, At trend	$ 4,013	$ 5,308
Accumulated postretirement benefit obligation, At trend +1%	4,305	5,723
Impact of Accumulated postretirement benefit obligation, At trend +1%	$ 292	$ 415
Impact of Accumulated postretirement benefit obligation, At trend +1% (as a percent)	7.30%	7.80%
Accumulated postretirement benefit obligation, At trend -1%	$ 3,755	$ 4,944
Impact of Accumulated postretirement benefit obligation, At trend -1%	$ (258)	$ (364)
Impact of Accumulated postretirement benefit obligation, At trend -1% (as a percent)	(6.40%)	(6.90%)
Service cost plus interest cost, At trend	$ 308	$ 389
Service cost plus interest cost, At Trend +1%	338	429
Impact of Service cost plus interest cost, At trend +1%	$ 30	$ 40
Impact of Service cost plus interest cost, At trend +1% (as a percent)	9.70%	10.30%
Service cost plus interest cost, At Trend -1%	$ 282	$ 355
Impact of Service cost plus interest cost, At trend -1%	$ (26)	$ (34)
Impact of Service cost plus interest cost, At trend -1% (as a percent)	(8.40%)	(8.70%)
Pension Plans
Weighted-average rates assumed in the actuarial calculations for the pension plan
Discount rate for benefit obligation (as percent)	4.70%	4.20%	4.60%
Discount rate for benefit cost (as percent)	4.30%	4.60%	4.30%
Annual salary increase (as a percent)	6.50%	6.50%	6.50%
Expected long-term return on plan assets (as a percent)	6.10%	6.10%	6.30%
Postretirement Benefits
Weighted-average rates assumed in the actuarial calculations for the pension plan
Discount rate for benefit obligation (as percent)	4.50%	3.90%	4.30%
Discount rate for benefit cost (as percent)	3.90%	4.30%	3.90%
Postretirement Benefits \| Medical benefit plan
Health care cost trend rates
2019 Trend rate	6.00%
Ultimate rate	4.00%
Postretirement Benefits \| Dental benefit plan
Health care cost trend rates
2019 Trend rate	4.00%
Ultimate rate	4.00%

For defined benefit pension plans, the actuarial present value of benefits decreased one percentage point 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.

No definition available.