BENEFIT PLANS (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension Benefits [Member]
Net periodic benefit cost [Abstract]
Service cost	$ 1,270		$ 1,154	$ 3,811	$ 3,396
Interest cost	1,566		1,422	4,698	4,251
Expected return on plan assets	(3,578)		(3,705)	(10,733)	(11,115)
Amortization of unrecognized net loss	642		299	1,926	895
Amortization of prior service cost	17		(60)	48	(225)
Net periodic benefit	(83)		(890)	(250)	(2,798)
Pension Benefits [Member] | Nonqualified Plan [Member] | Unfunded Plan [Member]
Pension Plans [Abstract]
Contribution made to defined benefit pension plan by employer		$ 7,300
Unfunded initial projected benefit obligation	800			800
Post-retirement Benefits [Member]
Net periodic benefit cost [Abstract]
Service cost	0		0	0	0
Interest cost	18		18	53	52
Expected return on plan assets	0		0	0	0
Amortization of unrecognized net loss	9		5	28	15
Amortization of prior service cost	(45)		(45)	(134)	(134)
Net periodic benefit	$ (18)		$ (22)	$ (53)	$ (67)