BENEFIT PLANS (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Pension Benefits [Member]
Net periodic benefit cost [Abstract]
Service cost	$ 1,438	$ 1,270
Interest cost	1,356	1,566
Expected return on plan assets	(3,932)	(3,577)
Amortization of unrecognized net loss	810	642
Amortization of prior service cost	60	16
Net periodic benefit	(268)	(83)
Pension Benefits [Member] | Nonqualified Plan [Member] | Unfunded Plan [Member]
Pension Plans [Abstract]
Contribution made to defined benefit pension plan by employer	0	7,300
Post-retirement Benefits [Member]
Net periodic benefit cost [Abstract]
Service cost	0	0
Interest cost	14	18
Expected return on plan assets	0	0
Amortization of unrecognized net loss	10	9
Amortization of prior service cost	(45)	(45)
Net periodic benefit	$ (21)	$ (18)