LOANS AND ALLOWANCE FOR LOAN LOSSES (Credit Risk Exposure Indicators by Portfolio Segment) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 2,908,843	$ 2,782,439	$ 2,748,290
Pass (Grades 1-6)
Financing Receivable, Recorded Investment [Line Items]
Loans	2,512,366	2,374,582
Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	344,051	339,876
Special Mention (Grade 7)
Financing Receivable, Recorded Investment [Line Items]
Loans	16,937	22,784
Substandard (Grade 8)
Financing Receivable, Recorded Investment [Line Items]
Loans	33,830	43,546
Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans	1,659	1,651
Residential Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans	941,488	858,369	852,851
Residential Real Estate | Pass (Grades 1-6)
Financing Receivable, Recorded Investment [Line Items]
Loans	930,134	846,394
Residential Real Estate | Special Mention (Grade 7)
Financing Receivable, Recorded Investment [Line Items]
Loans	897	922
Residential Real Estate | Substandard (Grade 8)
Financing Receivable, Recorded Investment [Line Items]
Loans	10,457	11,053
Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans	1,215,979	1,164,023	1,131,883
Commercial Real Estate | Pass (Grades 1-6)
Financing Receivable, Recorded Investment [Line Items]
Loans	1,185,948	1,130,235
Commercial Real Estate | Special Mention (Grade 7)
Financing Receivable, Recorded Investment [Line Items]
Loans	13,099	9,154
Commercial Real Estate | Substandard (Grade 8)
Financing Receivable, Recorded Investment [Line Items]
Loans	16,932	24,634
Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	368,837	373,400	369,155
Commercial | Pass (Grades 1-6)
Financing Receivable, Recorded Investment [Line Items]
Loans	360,959	354,904
Commercial | Special Mention (Grade 7)
Financing Receivable, Recorded Investment [Line Items]
Loans	2,802	12,517
Commercial | Substandard (Grade 8)
Financing Receivable, Recorded Investment [Line Items]
Loans	5,076	5,979
Home Equity
Financing Receivable, Recorded Investment [Line Items]
Loans	325,452	323,378	328,328
Home Equity | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	323,840	321,727
Home Equity | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans	1,612	1,651
Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	20,258	18,149	18,123
Consumer | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	20,211	18,149
Consumer | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans	47
HPFC Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Loans	36,829	45,120	$ 47,950
HPFC Portfolio Segment | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	35,325	43,049
HPFC Portfolio Segment | Substandard (Grade 8)
Financing Receivable, Recorded Investment [Line Items]
Loans	139	191
HPFC Portfolio Segment | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 1,365	$ 1,880