BENEFIT PLANS (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension Benefits [Member]
Net periodic benefit cost [Abstract]
Service cost	$ 1,438	$ 1,270		$ 4,313	$ 3,811
Interest cost	1,356	1,566		4,068	4,698
Expected return on plan assets	(3,932)	(3,578)		(11,796)	(10,733)
Amortization of unrecognized net loss	810	642		2,430	1,926
Amortization of prior service cost	60	17		180	48
Net periodic benefit	(268)	(83)		(805)	(250)
Pension Benefits [Member] | Nonqualified Plan [Member] | Unfunded Plan [Member]
Pension Plans [Abstract]
Contribution made to defined benefit pension plan by employer	3,900		$ 7,300
Post-retirement Benefits [Member]
Net periodic benefit cost [Abstract]
Service cost	0	0		0	0
Interest cost	15	18		43	53
Expected return on plan assets	0	0		0	0
Amortization of unrecognized net loss	10	9		30	28
Amortization of prior service cost	(45)	(45)		(134)	(134)
Net periodic benefit	(20)	$ (18)		$ (61)	$ (53)
Steuben Trust Company Pension Plan
Pension Plans [Abstract]
Contribution made to defined benefit pension plan by employer	$ 3,500