BENEFIT PLANS (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Pension Benefits [Member]
Net periodic benefit cost [Abstract]
Service cost	$ 1,270	$ 1,121
Interest cost	1,566	1,415
Expected return on plan assets	(3,577)	(3,705)
Amortization of unrecognized net loss	642	298
Amortization of prior service cost	16	(83)
Net periodic benefit	(83)	(954)
Pension Benefits [Member] | Nonqualified Plan [Member] | Unfunded Plan [Member]
Pension Plans [Abstract]
Unfunded initial projected benefit obligation	800
Contribution made to defined benefit pension plan by employer	7,300
Post-retirement Benefits [Member]
Net periodic benefit cost [Abstract]
Service cost	0	0
Interest cost	18	17
Expected return on plan assets	0	0
Amortization of unrecognized net loss	9	5
Amortization of prior service cost	(45)	(44)
Net periodic benefit	$ (18)	$ (22)