LOANS AND ALLOWANCE FOR LOAN LOSSES (Credit Risk Exposure Indicators by Portfolio Segment) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 2,789,148	$ 2,782,439	$ 2,645,139
Pass (Grades 1-6)
Financing Receivable, Recorded Investment [Line Items]
Loans	2,396,914	2,374,582
Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	337,189	339,876
Special Mention (Grade 7)
Financing Receivable, Recorded Investment [Line Items]
Loans	21,783	22,784
Substandard (Grade 8)
Financing Receivable, Recorded Investment [Line Items]
Loans	31,798	43,546
Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans	1,464	1,651
Residential Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans	860,533	858,369	819,639
Residential Real Estate | Pass (Grades 1-6)
Financing Receivable, Recorded Investment [Line Items]
Loans	847,822	846,394
Residential Real Estate | Special Mention (Grade 7)
Financing Receivable, Recorded Investment [Line Items]
Loans	662	922
Residential Real Estate | Substandard (Grade 8)
Financing Receivable, Recorded Investment [Line Items]
Loans	12,049	11,053
Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans	1,169,533	1,164,023	1,096,475
Commercial Real Estate | Pass (Grades 1-6)
Financing Receivable, Recorded Investment [Line Items]
Loans	1,146,947	1,130,235
Commercial Real Estate | Special Mention (Grade 7)
Financing Receivable, Recorded Investment [Line Items]
Loans	8,510	9,154
Commercial Real Estate | Substandard (Grade 8)
Financing Receivable, Recorded Investment [Line Items]
Loans	14,076	24,634
Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	378,015	373,400	333,607
Commercial | Pass (Grades 1-6)
Financing Receivable, Recorded Investment [Line Items]
Loans	361,377	354,904
Commercial | Special Mention (Grade 7)
Financing Receivable, Recorded Investment [Line Items]
Loans	12,437	12,517
Commercial | Substandard (Grade 8)
Financing Receivable, Recorded Investment [Line Items]
Loans	4,201	5,979
Home Equity
Financing Receivable, Recorded Investment [Line Items]
Loans	320,642	323,378	322,826
Home Equity | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	319,178	321,727
Home Equity | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans	1,464	1,651
Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	18,011	18,149	16,669
Consumer | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	18,011	18,149
HPFC Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Loans	42,414	45,120	$ 55,923
HPFC Portfolio Segment | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	40,768	43,049
HPFC Portfolio Segment | Substandard (Grade 8)
Financing Receivable, Recorded Investment [Line Items]
Loans	174	191
HPFC Portfolio Segment | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 1,472	$ 1,880