PENSION AND POSTRETIREMENT PLANS - Components of Net Periodic Benefit Cost (Credit): (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension Benefits
Components of net periodic benefit (credit) cost and other amounts recognized in other comprehensive income:
Service cost	$ 265	$ 273	$ 795	$ 818
Interest cost	193	225	578	675
Expected return on plan assets	(713)	(608)	(2,138)	(1,823)
Amortization of net loss	100	130	300	390
Amortization of prior service credit	(20)	(20)	(58)	(58)
Net periodic benefit (credit) cost	(175)		(523)	2
SERP Benefits
Components of net periodic benefit (credit) cost and other amounts recognized in other comprehensive income:
Service cost	92	65	278	196
Interest cost	38	37	112	110
Expected return on plan assets	0	0	0	0
Amortization of net loss	56	18	170	53
Amortization of prior service credit	0	0	0	0
Net periodic benefit (credit) cost	$ 186	$ 120	$ 560	$ 359