BENEFIT PLANS (Details) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	May 12, 2017	Dec. 31, 2016
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Tax Status [Extensible List]	us-gaap:QualifiedPlanMember				us-gaap:QualifiedPlanMember
Unamortized actuarial gain							$ 1,900
Discount rate							4.40%	4.50%
Employer contributions			$ 2,900
Net periodic benefit cost [Abstract]
Service cost	$ 1,037			$ 1,027	$ 3,143	$ 3,079
Interest cost	1,453			1,406	4,265	4,218
Expected return on plan assets	(3,448)			(2,961)	(9,977)	(8,882)
Amortization of unrecognized net loss	148			377	619	1,131
Amortization of prior service cost	13			11	43	33
Net periodic benefit cost (income)	(797)			(140)	(1,907)	(421)
Post-retirement Benefits [Member]
Net periodic benefit cost [Abstract]
Service cost	0			0	0	0
Interest cost	19			20	57	61
Expected return on plan assets	0			0	0	0
Amortization of unrecognized net loss	2			(1)	6	(4)
Amortization of prior service cost	(45)			(45)	(134)	(134)
Net periodic benefit cost (income)	$ (24)			$ (26)	$ (71)	$ (77)
Merchants Bancshares, Inc. [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions		$ 2,000