EMPLOYEE RETIREMENT PLANS - Components of Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Components of net periodic pension cost [Abstract]
Service cost	$ 1,092	$ 969
Interest cost	1,285	1,613
Supplemental Executive Retirement Plan [Member]
Components of net periodic pension cost [Abstract]
Service cost	1,092	969	$ 1,301
Interest cost	1,285	1,613	1,047
Amortization of prior service cost	1,098	1,595	1,683
Amortization of loss	2,181	1,641	435
Total net periodic benefit cost	$ 5,656	$ 5,818	$ 4,466