LOANS AND ALLOWANCE FOR LOAN LOSSES (Credit Risk Exposure Indicators by Portfolio Segment) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 3,157,762	$ 3,095,023	$ 3,042,442
Pass (Grades 1-6)
Financing Receivable, Recorded Investment [Line Items]
Loans	2,768,801	2,696,045
Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	328,503	336,401
Special Mention (Grade 7)
Financing Receivable, Recorded Investment [Line Items]
Loans	32,998	34,859
Substandard (Grade 8)
Financing Receivable, Recorded Investment [Line Items]
Loans	25,360	25,568
Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans	2,100	2,150
Residential Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans	1,064,212	1,070,374	1,017,442
Residential Real Estate | Pass (Grades 1-6)
Financing Receivable, Recorded Investment [Line Items]
Loans	1,057,552	1,062,825
Residential Real Estate | Special Mention (Grade 7)
Financing Receivable, Recorded Investment [Line Items]
Loans	469	473
Residential Real Estate | Substandard (Grade 8)
Financing Receivable, Recorded Investment [Line Items]
Loans	6,191	7,076
Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans	1,299,860	1,243,397	1,258,474
Commercial Real Estate | Pass (Grades 1-6)
Financing Receivable, Recorded Investment [Line Items]
Loans	1,254,201	1,196,683
Commercial Real Estate | Special Mention (Grade 7)
Financing Receivable, Recorded Investment [Line Items]
Loans	31,028	31,753
Commercial Real Estate | Substandard (Grade 8)
Financing Receivable, Recorded Investment [Line Items]
Loans	14,631	14,961
Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	444,830	421,108	390,982
Commercial | Pass (Grades 1-6)
Financing Receivable, Recorded Investment [Line Items]
Loans	439,638	415,870
Commercial | Special Mention (Grade 7)
Financing Receivable, Recorded Investment [Line Items]
Loans	1,424	2,544
Commercial | Substandard (Grade 8)
Financing Receivable, Recorded Investment [Line Items]
Loans	3,768	2,694
Home Equity
Financing Receivable, Recorded Investment [Line Items]
Loans	306,226	312,779	323,969
Home Equity | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	304,131	310,653
Home Equity | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans	2,095	2,126
Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	24,377	25,772	20,733
Consumer | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	24,372	25,748
Consumer | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans	5	24
HPFC Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Loans	18,257	21,593	$ 30,842
HPFC Portfolio Segment | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	17,410	20,667
HPFC Portfolio Segment | Substandard (Grade 8)
Financing Receivable, Recorded Investment [Line Items]
Loans	77	89
HPFC Portfolio Segment | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 770	$ 837