RETIREMENT PLANS - Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Components of the plan's net periodic pension cost
Company contributions			$ 300	$ 2,100
Pension Plans
Components of the plan's net periodic pension cost
Service cost	$ 447	$ 448	1,342	1,345
Interest cost	841	820	2,524	2,459
Expected return on plan assets	(1,263)	(1,209)	(3,790)	(3,627)
Actuarial gain/ loss	7	30	22	91
Net periodic pension expense	32	89	98	268
Postretirement Benefits
Components of the plan's net periodic pension cost
Service cost	37	37	111	111
Interest cost	40	40	120	120
Actuarial gain/ loss	(17)	(17)	(51)	(51)
Net periodic pension expense	$ 60	$ 60	$ 180	$ 180