LOANS AND ALLOWANCE FOR LOAN LOSSES (Activity in Allowance for Loan Losses by Portfolio Segment) (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Reserve for unfunded commitments	$ 15,000	$ 22,000	$ 15,000	$ 22,000	$ 20,000
Activity in ALL:
Beginning balance	23,668,000	24,394,000	24,171,000	23,116,000	23,116,000
Loans charged off	(659,000)	(908,000)	(1,851,000)	(1,931,000)	(2,468,000)
Recoveries	162,000	125,000	361,000	442,000	497,000
Provision (credit)(1)	355,000	802,000	845,000	2,786,000	3,026,000
Ending balance	23,526,000	24,413,000	23,526,000	24,413,000	24,171,000
Ending Balance: Individually evaluated for impairment	756,000	1,934,000	756,000	1,934,000	2,009,000
Ending Balance: Collectively evaluated for impairment	22,770,000	22,479,000	22,770,000	22,479,000	22,162,000
Ending Balance: Individually evaluated for impairment	12,112,000	13,430,000	12,112,000	13,430,000	13,590,000
Ending Balance: Collectively evaluated for impairment	2,896,731,000	2,734,860,000	2,896,731,000	2,734,860,000	2,768,849,000
Total Loans Outstanding	2,908,843,000	2,748,290,000	2,908,843,000	2,748,290,000	2,782,439,000
Residential Real Estate
Activity in ALL:
Beginning balance	5,779,000	4,481,000	5,086,000	4,160,000	4,160,000
Loans charged off	(115,000)	(238,000)	(231,000)	(433,000)	(482,000)
Recoveries	37,000	26,000	52,000	30,000	30,000
Provision (credit)(1)	59,000	273,000	853,000	785,000	1,378,000
Ending balance	5,760,000	4,542,000	5,760,000	4,542,000	5,086,000
Ending Balance: Individually evaluated for impairment	619,000	464,000	619,000	464,000	568,000
Ending Balance: Collectively evaluated for impairment	5,141,000	4,078,000	5,141,000	4,078,000	4,518,000
Ending Balance: Individually evaluated for impairment	5,184,000	4,792,000	5,184,000	4,792,000	5,171,000
Ending Balance: Collectively evaluated for impairment	936,304,000	848,059,000	936,304,000	848,059,000	853,198,000
Total Loans Outstanding	941,488,000	852,851,000	941,488,000	852,851,000	858,369,000
Commercial Real Estate
Activity in ALL:
Beginning balance	10,310,000	12,848,000	11,863,000	12,154,000	12,154,000
Loans charged off	0	(69,000)	(512,000)	(81,000)	(124,000)
Recoveries	4,000	25,000	19,000	138,000	141,000
Provision (credit)(1)	268,000	(8,000)	(788,000)	585,000	(308,000)
Ending balance	10,582,000	12,796,000	10,582,000	12,796,000	11,863,000
Ending Balance: Individually evaluated for impairment	23,000	1,470,000	23,000	1,470,000	1,441,000
Ending Balance: Collectively evaluated for impairment	10,559,000	11,326,000	10,559,000	11,326,000	10,422,000
Ending Balance: Individually evaluated for impairment	5,007,000	6,373,000	5,007,000	6,373,000	6,199,000
Ending Balance: Collectively evaluated for impairment	1,210,972,000	1,125,510,000	1,210,972,000	1,125,510,000	1,157,824,000
Total Loans Outstanding	1,215,979,000	1,131,883,000	1,215,979,000	1,131,883,000	1,164,023,000
Commercial
Activity in ALL:
Beginning balance	4,303,000	4,275,000	4,171,000	3,755,000	3,755,000
Loans charged off	(150,000)	(369,000)	(448,000)	(650,000)	(1,014,000)
Recoveries	117,000	59,000	237,000	254,000	301,000
Provision (credit)(1)	(302,000)	256,000	8,000	862,000	1,129,000
Ending balance	3,968,000	4,221,000	3,968,000	4,221,000	4,171,000
Ending Balance: Individually evaluated for impairment	0	0	0	0
Ending Balance: Collectively evaluated for impairment	3,968,000	4,221,000	3,968,000	4,221,000	4,171,000
Ending Balance: Individually evaluated for impairment	1,548,000	1,842,000	1,548,000	1,842,000	1,791,000
Ending Balance: Collectively evaluated for impairment	367,289,000	367,313,000	367,289,000	367,313,000	371,609,000
Total Loans Outstanding	368,837,000	369,155,000	368,837,000	369,155,000	373,400,000
Home Equity
Activity in ALL:
Beginning balance	2,616,000	2,094,000	2,367,000	2,194,000	2,194,000
Loans charged off	(157,000)	(11,000)	(381,000)	(403,000)	(434,000)
Recoveries	0	1,000	44,000	2,000	2,000
Provision (credit)(1)	116,000	93,000	545,000	384,000	605,000
Ending balance	2,575,000	2,177,000	2,575,000	2,177,000	2,367,000
Ending Balance: Individually evaluated for impairment	114,000	0	114,000	0
Ending Balance: Collectively evaluated for impairment	2,461,000	2,177,000	2,461,000	2,177,000	2,367,000
Ending Balance: Individually evaluated for impairment	373,000	423,000	373,000	423,000	429,000
Ending Balance: Collectively evaluated for impairment	325,079,000	327,905,000	325,079,000	327,905,000	322,949,000
Total Loans Outstanding	325,452,000	328,328,000	325,452,000	328,328,000	323,378,000
Consumer
Activity in ALL:
Beginning balance	260,000	182,000	233,000	181,000	181,000
Loans charged off	(28,000)	(28,000)	(70,000)	(90,000)	(124,000)
Recoveries	3,000	9,000	8,000	13,000	17,000
Provision (credit)(1)	38,000	32,000	102,000	91,000	159,000
Ending balance	273,000	195,000	273,000	195,000	233,000
Ending Balance: Individually evaluated for impairment	0	0	0	0
Ending Balance: Collectively evaluated for impairment	273,000	195,000	273,000	195,000	233,000
Ending Balance: Individually evaluated for impairment	0	0	0	0
Ending Balance: Collectively evaluated for impairment	20,258,000	18,123,000	20,258,000	18,123,000	18,149,000
Total Loans Outstanding	20,258,000	18,123,000	20,258,000	18,123,000	18,149,000
HPFC Portfolio Segment
Activity in ALL:
Beginning balance	400,000	514,000	451,000	672,000	672,000
Loans charged off	(209,000)	(193,000)	(209,000)	(274,000)	(290,000)
Recoveries	1,000	5,000	1,000	5,000	6,000
Provision (credit)(1)	176,000	156,000	125,000	79,000	63,000
Ending balance	368,000	482,000	368,000	482,000	451,000
Ending Balance: Individually evaluated for impairment	0	0	0	0
Ending Balance: Collectively evaluated for impairment	368,000	482,000	368,000	482,000	451,000
Ending Balance: Individually evaluated for impairment	0	0	0	0
Ending Balance: Collectively evaluated for impairment	36,829,000	47,950,000	36,829,000	47,950,000	45,120,000
Total Loans Outstanding	$ 36,829,000	$ 47,950,000	$ 36,829,000	$ 47,950,000	$ 45,120,000