LOANS AND ALLOWANCE FOR LOAN LOSSES (Loan Aging Analysis by Portfolio Segment) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 13,817	$ 12,089
Current	3,143,945	3,082,934
Total Loans Outstanding	3,157,762	3,095,023	$ 3,042,442
Loans 90 Days Past Due and Accruing	0	0
Non-Accrual Loans	7,317	8,156
Residential Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,543	5,522
Current	1,059,669	1,064,852
Total Loans Outstanding	1,064,212	1,070,374	1,017,442
Loans 90 Days Past Due and Accruing	0	0
Non-Accrual Loans	3,499	4,096
Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,145	2,531
Current	1,296,715	1,240,866
Total Loans Outstanding	1,299,860	1,243,397	1,258,474
Loans 90 Days Past Due and Accruing	0	0
Non-Accrual Loans	646	1,122
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,305	965
Current	442,525	420,143
Total Loans Outstanding	444,830	421,108	390,982
Loans 90 Days Past Due and Accruing	0	0
Non-Accrual Loans	748	420
Home Equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,313	2,378
Current	302,913	310,401
Total Loans Outstanding	306,226	312,779	323,969
Loans 90 Days Past Due and Accruing	0	0
Non-Accrual Loans	2,098	2,130
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	94	162
Current	24,283	25,610
Total Loans Outstanding	24,377	25,772	20,733
Loans 90 Days Past Due and Accruing	0	0
Non-Accrual Loans	4	24
HPFC Portfolio Segment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	417	531
Current	17,840	21,062
Total Loans Outstanding	18,257	21,593	$ 30,842
Loans 90 Days Past Due and Accruing	0	0
Non-Accrual Loans	322	364
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,519	3,901
30-59 Days Past Due | Residential Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,778	2,297
30-59 Days Past Due | Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,207	267
30-59 Days Past Due | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,315	548
30-59 Days Past Due | Home Equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,140	681
30-59 Days Past Due | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	58	108
30-59 Days Past Due | HPFC Portfolio Segment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	21	0
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,773	2,859
60-89 Days Past Due | Residential Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	320	627
60-89 Days Past Due | Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,460	1,720
60-89 Days Past Due | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	388	0
60-89 Days Past Due | Home Equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	430	238
60-89 Days Past Due | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	31	31
60-89 Days Past Due | HPFC Portfolio Segment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	144	243
Greater than 90 Days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,525	5,329
Greater than 90 Days | Residential Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,445	2,598
Greater than 90 Days | Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	478	544
Greater than 90 Days | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	602	417
Greater than 90 Days | Home Equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,743	1,459
Greater than 90 Days | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5	23
Greater than 90 Days | HPFC Portfolio Segment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 252	$ 288