LOANS AND ALLOWANCE FOR LOAN LOSSES (Narrative) (Details)	3 Months Ended
	Mar. 31, 2018 USD ($) loan	Mar. 31, 2017 USD ($) loan	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	$ 14,898,000		$ 15,314,000
Other industry exposures	0
Interest lost on nonaccrual loans	$ 162,000	$ 210,000
Number of TDRs | loan	0	1
Loans modified | loan	0	0
Financing Receivable, Individually Evaluated for Impairment	$ 11,225,000	$ 20,128,000	13,590,000
Proceeds from the sale of mortgage loans	46,426,000	44,320,000
Gain on sale of mortgage loans	1,220,000	1,280,000
Loans held for sale, at fair value	9,548,000		8,103,000
Financing Receivable, Allowance for Credit Losses	22,990,000	23,721,000	24,171,000	$ 23,116,000
FHLB advances, general debt obligations, pledged collateral	1,100,000,000		1,100,000,000
Derivative, Fair Value, Net	123,000		142,000
Unrealized Gain (Loss) on Derivatives	(12,000)	(12,000)
Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans restructured due to credit difficulties that are now performing	4,400,000		5,000,000
Financing receivables impaired TDR non-performing	1,200,000		1,200,000
Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	6,185,000		4,979,000
Financing Receivable, Individually Evaluated for Impairment	5,059,000	4,408,000	5,171,000
Mortgage Loans in Process of Foreclosure, Amount	2,000,000		1,900,000
Financing Receivable, Allowance for Credit Losses	5,497,000	4,271,000	5,086,000	4,160,000
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	4,603,000		5,642,000
Financing Receivable, Individually Evaluated for Impairment	3,961,000	13,191,000	6,199,000
Financing Receivable, Allowance for Credit Losses	10,286,000	12,726,000	11,863,000	12,154,000
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	1,991,000		2,000,000
Financing Receivable, Individually Evaluated for Impairment	1,714,000	1,994,000	1,791,000
Financing Receivable, Allowance for Credit Losses	4,126,000	3,815,000	4,171,000	3,755,000
Home Equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	1,464,000		1,650,000
Financing Receivable, Individually Evaluated for Impairment	491,000	430,000	429,000
Financing Receivable, Allowance for Credit Losses	2,427,000	2,107,000	2,367,000	2,194,000
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	0		0
Financing Receivable, Individually Evaluated for Impairment	0	7,000
Financing Receivable, Allowance for Credit Losses	230,000	175,000	233,000	181,000
HPFC Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	655,000		1,043,000
Financing Receivable, Individually Evaluated for Impairment	0	98,000
Financing Receivable, Allowance for Credit Losses	424,000	627,000	451,000	$ 672,000
Fixed Rate Residential Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from the sale of mortgage loans	45,200,000	43,000,000
Gain on sale of mortgage loans	1,200,000	1,300,000
Loans held for sale, at fair value	9,500,000		8,100,000
Nonoperating Income (Expense) | Fixed Rate Residential Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gain on sale of mortgage loans	9,000	254,000
Unrealized gain (loss) on loans held for sale	$ 47,000	37,000
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Individually Evaluated for Impairment			250,000
Number of Months	18
Minimum | HPFC Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term to maturity	7 years
Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Months	24
Maximum | HPFC Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term to maturity	10 years
Non-Residential Building Operators Industry Sector | Loan Concentration Risk | Total Loan Portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk (percentage)	11.00%
Non-Residential Building Operators Industry Sector | Loan Concentration Risk | Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk (percentage)	26.00%
Substandard (Grade 8) | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Individually Evaluated for Impairment	$ 500,000
Forward Contracts [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Derivative, Fair Value, Net	123,000		$ 142,000
Unrealized Gain (Loss) on Derivatives	$ 19,000	$ 118,000