LOANS AND ALLOWANCE FOR LOAN LOSSES (Credit Risk Exposure Indicators by Portfolio Segment) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 3,042,442	$ 3,026,222	$ 2,789,148
Pass (Grades 1-6)
Financing Receivable, Recorded Investment [Line Items]
Loans	2,659,869	2,636,966
Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	342,215	346,512
Special Mention (Grade 7)
Financing Receivable, Recorded Investment [Line Items]
Loans	8,248	12,619
Substandard (Grade 8)
Financing Receivable, Recorded Investment [Line Items]
Loans	29,623	28,250
Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans	2,487	1,875
Residential Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans	1,017,442	992,866	860,533
Residential Real Estate | Pass (Grades 1-6)
Financing Receivable, Recorded Investment [Line Items]
Loans	1,007,775	983,086
Residential Real Estate | Special Mention (Grade 7)
Financing Receivable, Recorded Investment [Line Items]
Loans	878	887
Residential Real Estate | Substandard (Grade 8)
Financing Receivable, Recorded Investment [Line Items]
Loans	8,789	8,893
Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans	1,258,474	1,269,533	1,169,533
Commercial Real Estate | Pass (Grades 1-6)
Financing Receivable, Recorded Investment [Line Items]
Loans	1,237,494	1,247,190
Commercial Real Estate | Special Mention (Grade 7)
Financing Receivable, Recorded Investment [Line Items]
Loans	5,114	7,921
Commercial Real Estate | Substandard (Grade 8)
Financing Receivable, Recorded Investment [Line Items]
Loans	15,866	14,422
Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	390,982	381,780	378,015
Commercial | Pass (Grades 1-6)
Financing Receivable, Recorded Investment [Line Items]
Loans	385,081	374,429
Commercial | Special Mention (Grade 7)
Financing Receivable, Recorded Investment [Line Items]
Loans	2,146	3,688
Commercial | Substandard (Grade 8)
Financing Receivable, Recorded Investment [Line Items]
Loans	3,755	3,663
Home Equity
Financing Receivable, Recorded Investment [Line Items]
Loans	323,969	327,763	320,642
Home Equity | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	321,505	325,917
Home Equity | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans	2,464	1,846
Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	20,733	20,624	18,011
Consumer | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	20,710	20,595
Consumer | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans	23	29
HPFC Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Loans	30,842	33,656	$ 42,414
HPFC Portfolio Segment | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	29,519	32,261
HPFC Portfolio Segment | Substandard (Grade 8)
Financing Receivable, Recorded Investment [Line Items]
Loans	110	123
HPFC Portfolio Segment | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 1,213	$ 1,272