LOANS AND ALLOWANCE FOR LOAN AND LEASE LOSSES - TDR MODIFICATIONS (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2018 USD ($) item	Mar. 31, 2017 USD ($) item	Dec. 31, 2017 USD ($) item
Troubled Debt Restructurings disclosures
Number of Loans | item	1,094		1,097
Recorded Investment	$ 34,745,000		$ 34,637,000
Commitments to lend any additional material amounts to existing TDR relationships	$ 0		$ 0
Residential Real Estate
Troubled Debt Restructurings disclosures
Number of Loans | item	242		245
Recorded Investment	$ 25,763,000		$ 25,115,000
Residential Real Estate | Interest only payments
Troubled Debt Restructurings disclosures
Number of Loans | item	1		2
Recorded Investment	$ 4,000		$ 463,000
Residential Real Estate | Rate reduction
Troubled Debt Restructurings disclosures
Number of Loans | item	178		179
Recorded Investment	$ 20,367,000		$ 20,698,000
Residential Real Estate | Principal deferral
Troubled Debt Restructurings disclosures
Number of Loans | item	16		15
Recorded Investment	$ 3,249,000		$ 1,557,000
Residential Real Estate | Legal modifications
Troubled Debt Restructurings disclosures
Number of Loans | item	47		49
Recorded Investment	$ 2,143,000		$ 2,397,000
Commercial Real Estate and Commercial Construction
Troubled Debt Restructurings disclosures
Number of Loans | item	24		22
Recorded Investment	$ 8,497,000		$ 8,885,000
Commercial Real Estate and Commercial Construction | Interest only payments
Troubled Debt Restructurings disclosures
Number of Loans | item	3		3
Recorded Investment	$ 808,000		$ 837,000
Commercial Real Estate and Commercial Construction | Rate reduction
Troubled Debt Restructurings disclosures
Number of Loans | item	8		8
Recorded Investment	$ 3,203,000		$ 3,264,000
Commercial Real Estate and Commercial Construction | Principal deferral
Troubled Debt Restructurings disclosures
Number of Loans | item	13		11
Recorded Investment	$ 4,486,000		$ 4,784,000
Consumer and other | Principal deferral
Troubled Debt Restructurings disclosures
Number of Loans | item	828		830
Recorded Investment	$ 485,000		$ 637,000
Modified During The Period
Troubled Debt Restructurings disclosures
Number of Loans | item	7	3
Recorded Investment	$ 1,889,000	$ 197,000
Modified During The Period | Residential Real Estate
Troubled Debt Restructurings disclosures
Number of Loans | item	3	3
Recorded Investment	$ 1,811,000	$ 197,000
Modified During The Period | Residential Real Estate | Rate reduction
Troubled Debt Restructurings disclosures
Number of Loans | item	1	1
Recorded Investment	$ 85,000	$ 159,000
Modified During The Period | Residential Real Estate | Principal deferral
Troubled Debt Restructurings disclosures
Number of Loans | item	2
Recorded Investment	$ 1,726,000
Modified During The Period | Residential Real Estate | Legal modifications
Troubled Debt Restructurings disclosures
Number of Loans | item		2
Recorded Investment		$ 38,000
Modified During The Period | Commercial Real Estate and Commercial Construction
Troubled Debt Restructurings disclosures
Number of Loans | item	3
Recorded Investment	$ 17,000
Modified During The Period | Commercial Real Estate and Commercial Construction | Principal deferral
Troubled Debt Restructurings disclosures
Number of Loans | item	3
Recorded Investment	$ 17,000
Modified During The Period | Consumer and other | Principal deferral
Troubled Debt Restructurings disclosures
Number of Loans | item	1
Recorded Investment	$ 61,000
Performing Financing Receivable
Troubled Debt Restructurings disclosures
Number of Loans | item	1,026		1,031
Recorded Investment	$ 28,438,000		$ 28,265,000
Percentage of troubled debt restructurings performing as per terms of modifications	82.00%		82.00%
Specific reserve allocations made to customers	$ 3,000,000		$ 4,000,000
Percentage of Bank's TDRs that occurred during period, which were performing according to their modified terms	67.00%	100.00%
Specific reserve allocations made to customers whose loan terms were modified in TDRs during period	$ 127,000	$ 29,000
Performing Financing Receivable | Residential Real Estate
Troubled Debt Restructurings disclosures
Number of Loans | item	178		182
Recorded Investment	$ 20,873,000		$ 20,176,000
Performing Financing Receivable | Residential Real Estate | Interest only payments
Troubled Debt Restructurings disclosures
Number of Loans | item	1		1
Recorded Investment	$ 4,000		$ 5,000
Performing Financing Receivable | Residential Real Estate | Rate reduction
Troubled Debt Restructurings disclosures
Number of Loans | item	144		147
Recorded Investment	$ 17,205,000		$ 17,617,000
Performing Financing Receivable | Residential Real Estate | Principal deferral
Troubled Debt Restructurings disclosures
Number of Loans | item	13		13
Recorded Investment	$ 2,610,000		$ 1,436,000
Performing Financing Receivable | Residential Real Estate | Legal modifications
Troubled Debt Restructurings disclosures
Number of Loans | item	20		21
Recorded Investment	$ 1,054,000		$ 1,118,000
Performing Financing Receivable | Commercial Real Estate and Commercial Construction
Troubled Debt Restructurings disclosures
Number of Loans | item	20		19
Recorded Investment	$ 7,080,000		$ 7,452,000
Performing Financing Receivable | Commercial Real Estate and Commercial Construction | Interest only payments
Troubled Debt Restructurings disclosures
Number of Loans | item	3		3
Recorded Investment	$ 808,000		$ 837,000
Performing Financing Receivable | Commercial Real Estate and Commercial Construction | Rate reduction
Troubled Debt Restructurings disclosures
Number of Loans | item	7		7
Recorded Investment	$ 3,125,000		$ 3,185,000
Performing Financing Receivable | Commercial Real Estate and Commercial Construction | Principal deferral
Troubled Debt Restructurings disclosures
Number of Loans | item	10		9
Recorded Investment	$ 3,147,000		$ 3,430,000
Performing Financing Receivable | Consumer and other | Principal deferral
Troubled Debt Restructurings disclosures
Number of Loans | item	828		830
Recorded Investment	$ 485,000		$ 637,000
Performing Financing Receivable | Modified During The Period
Troubled Debt Restructurings disclosures
Number of Loans | item	4	3
Recorded Investment	$ 1,268,000	$ 197,000
Performing Financing Receivable | Modified During The Period | Residential Real Estate
Troubled Debt Restructurings disclosures
Number of Loans | item	1	3
Recorded Investment	$ 1,204,000	$ 197,000
Performing Financing Receivable | Modified During The Period | Residential Real Estate | Rate reduction
Troubled Debt Restructurings disclosures
Number of Loans | item		1
Recorded Investment		$ 159,000
Performing Financing Receivable | Modified During The Period | Residential Real Estate | Principal deferral
Troubled Debt Restructurings disclosures
Number of Loans | item	1
Recorded Investment	$ 1,204,000
Performing Financing Receivable | Modified During The Period | Residential Real Estate | Legal modifications
Troubled Debt Restructurings disclosures
Number of Loans | item		2
Recorded Investment		$ 38,000
Performing Financing Receivable | Modified During The Period | Commercial Real Estate and Commercial Construction
Troubled Debt Restructurings disclosures
Number of Loans | item	2
Recorded Investment	$ 3,000
Performing Financing Receivable | Modified During The Period | Commercial Real Estate and Commercial Construction | Principal deferral
Troubled Debt Restructurings disclosures
Number of Loans | item	2
Recorded Investment	$ 3,000
Performing Financing Receivable | Modified During The Period | Consumer and other | Principal deferral
Troubled Debt Restructurings disclosures
Number of Loans | item	1
Recorded Investment	$ 61,000
Nonperforming Financing Receivable
Troubled Debt Restructurings disclosures
Number of Loans | item	68		66
Recorded Investment	$ 6,307,000		$ 6,372,000
Nonperforming Financing Receivable | Residential Real Estate
Troubled Debt Restructurings disclosures
Number of Loans | item	64		63
Recorded Investment	$ 4,890,000		$ 4,939,000
Nonperforming Financing Receivable | Residential Real Estate | Interest only payments
Troubled Debt Restructurings disclosures
Number of Loans | item			1
Recorded Investment			$ 458,000
Nonperforming Financing Receivable | Residential Real Estate | Rate reduction
Troubled Debt Restructurings disclosures
Number of Loans | item	34		32
Recorded Investment	$ 3,162,000		$ 3,081,000
Nonperforming Financing Receivable | Residential Real Estate | Principal deferral
Troubled Debt Restructurings disclosures
Number of Loans | item	3		2
Recorded Investment	$ 639,000		$ 121,000
Nonperforming Financing Receivable | Residential Real Estate | Legal modifications
Troubled Debt Restructurings disclosures
Number of Loans | item	27		28
Recorded Investment	$ 1,089,000		$ 1,279,000
Nonperforming Financing Receivable | Commercial Real Estate and Commercial Construction
Troubled Debt Restructurings disclosures
Number of Loans | item	4		3
Recorded Investment	$ 1,417,000		$ 1,433,000
Nonperforming Financing Receivable | Commercial Real Estate and Commercial Construction | Rate reduction
Troubled Debt Restructurings disclosures
Number of Loans | item	1		1
Recorded Investment	$ 78,000		$ 79,000
Nonperforming Financing Receivable | Commercial Real Estate and Commercial Construction | Principal deferral
Troubled Debt Restructurings disclosures
Number of Loans | item	3		2
Recorded Investment	$ 1,339,000		$ 1,354,000
Nonperforming Financing Receivable | Modified During The Period
Troubled Debt Restructurings disclosures
Number of Loans | item	3
Recorded Investment	$ 621,000
Nonperforming Financing Receivable | Modified During The Period | Residential Real Estate
Troubled Debt Restructurings disclosures
Number of Loans | item	2
Recorded Investment	$ 607,000
Nonperforming Financing Receivable | Modified During The Period | Residential Real Estate | Rate reduction
Troubled Debt Restructurings disclosures
Number of Loans | item	1
Recorded Investment	$ 85,000
Nonperforming Financing Receivable | Modified During The Period | Residential Real Estate | Principal deferral
Troubled Debt Restructurings disclosures
Number of Loans | item	1
Recorded Investment	$ 522,000
Nonperforming Financing Receivable | Modified During The Period | Commercial Real Estate and Commercial Construction
Troubled Debt Restructurings disclosures
Number of Loans | item	1
Recorded Investment	$ 14,000
Nonperforming Financing Receivable | Modified During The Period | Commercial Real Estate and Commercial Construction | Principal deferral
Troubled Debt Restructurings disclosures
Number of Loans | item	1
Recorded Investment	$ 14,000