EMPLOYEE RETIREMENT PLANS - Schedule of components of net periodic pension cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
EMPLOYEE RETIREMENT PLANS
Service cost	$ 463	$ 569
Interest cost	2,460	2,204
Expected return on plan assets	(2,502)	(2,711)
Net amortization and deferral	626	634
Net periodic pension cost	$ 1,047	$ 696