BENEFIT PLANS (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Pension Benefits [Member]
Net periodic benefit cost [Abstract]
Service cost	$ 1,270		$ 1,121	$ 2,540	$ 2,242
Interest cost	1,565		1,415	3,133	2,829
Expected return on plan assets	(3,578)		(3,705)	(7,155)	(7,410)
Amortization of unrecognized net loss	643		298	1,284	596
Amortization of prior service cost	16		(83)	31	(165)
Net periodic benefit	(84)		(954)	(167)	(1,908)
Pension Benefits [Member] | Nonqualified Plan [Member] | Unfunded Plan [Member]
Pension Plans [Abstract]
Unfunded initial projected benefit obligation	800			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	0	0
Interest cost	18		17	35	34
Expected return on plan assets	0		0	0	0
Amortization of unrecognized net loss	9		5	19	10
Amortization of prior service cost	(45)		(44)	(89)	(89)
Net periodic benefit	$ (18)		$ (22)	$ (35)	$ (45)