EMPLOYEE BENEFIT PLANS - Other Postretirement Benefits (Details)	12 Months Ended
	Dec. 31, 2019 USD ($)
Other Postretirement Benefits | Maximum
EMPLOYEE BENEFIT PLANS
Age of eligibility for limited healthcare benefits	65 years
Group life insurance plan
EMPLOYEE BENEFIT PLANS
Face amount of life insurance benefits funded	$ 50,000
Benefit obligation, discount rate (as a percent)	3.38%
Net periodic benefit cost, discount rate (as a percent)	4.38%
Benefit obligation, expected long-term return on plan assets (as a percent)	2.50%
Period for which average and annualized return on short treasury index considered for long term rate of return assumption assessment	25 years
Group life insurance plan | Minimum
EMPLOYEE BENEFIT PLANS
Life insurance benefits	$ 10,000
Group life insurance plan | Maximum
EMPLOYEE BENEFIT PLANS
Life insurance benefits	$ 75,000