LOANS AND ALLOWANCE FOR LOAN LOSSES (Activity in Allowance for Loan Losses by Portfolio Segment) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]
Reserve for unfunded commitments	$ 16,000	$ 23,000	$ 22,000
Activity in ALL:
Beginning balance	24,712,000	24,171,000	24,171,000
Loans charged off	(336,000)	(803,000)	(2,248,000)
Recoveries	75,000	122,000	1,944,000
Provision (credit)(1)	750,000	(500,000)	845,000
Ending balance	25,201,000	22,990,000	24,712,000
Ending Balance: Individually evaluated for impairment	927,000	1,033,000	824,000
Ending Balance: Collectively evaluated for impairment	24,274,000	21,957,000	23,888,000
Ending Balance: Individually evaluated for impairment	6,264,000	11,225,000	6,926,000
Ending Balance: Collectively evaluated for impairment	3,036,178,000	2,777,923,000	3,019,296,000
Total Loans Outstanding	3,042,442,000	2,789,148,000	3,026,222,000
Residential Real Estate
Activity in ALL:
Beginning balance	6,071,000	5,086,000	5,086,000
Loans charged off	(11,000)	(31,000)	(173,000)
Recoveries	2,000	0	90,000
Provision (credit)(1)	91,000	442,000	1,068,000
Ending balance	6,153,000	5,497,000	6,071,000
Ending Balance: Individually evaluated for impairment	553,000	553,000	586,000
Ending Balance: Collectively evaluated for impairment	5,600,000	4,944,000	5,485,000
Ending Balance: Individually evaluated for impairment	4,736,000	5,059,000	4,762,000
Ending Balance: Collectively evaluated for impairment	1,012,706,000	855,474,000	988,104,000
Total Loans Outstanding	1,017,442,000	860,533,000	992,866,000
Commercial Real Estate
Activity in ALL:
Beginning balance	11,654,000	11,863,000	11,863,000
Loans charged off	(65,000)	(426,000)	(512,000)
Recoveries	4,000	13,000	28,000
Provision (credit)(1)	245,000	(1,164,000)	275,000
Ending balance	11,838,000	10,286,000	11,654,000
Ending Balance: Individually evaluated for impairment	27,000	368,000	23,000
Ending Balance: Collectively evaluated for impairment	11,811,000	9,918,000	11,631,000
Ending Balance: Individually evaluated for impairment	410,000	3,961,000	930,000
Ending Balance: Collectively evaluated for impairment	1,258,064,000	1,165,572,000	1,268,603,000
Total Loans Outstanding	1,258,474,000	1,169,533,000	1,269,533,000
Commercial
Activity in ALL:
Beginning balance	3,620,000	4,171,000	4,171,000
Loans charged off	(236,000)	(171,000)	(736,000)
Recoveries	62,000	63,000	1,770,000
Provision (credit)(1)	170,000	63,000	(1,585,000)
Ending balance	3,616,000	4,126,000	3,620,000
Ending Balance: Individually evaluated for impairment	0	0	53,000
Ending Balance: Collectively evaluated for impairment	3,616,000	4,126,000	3,567,000
Ending Balance: Individually evaluated for impairment	223,000	1,714,000	786,000
Ending Balance: Collectively evaluated for impairment	390,759,000	376,301,000	380,994,000
Total Loans Outstanding	390,982,000	378,015,000	381,780,000
Home Equity
Activity in ALL:
Beginning balance	2,796,000	2,367,000	2,367,000
Loans charged off	(10,000)	(149,000)	(476,000)
Recoveries	0	43,000	44,000
Provision (credit)(1)	241,000	166,000	861,000
Ending balance	3,027,000	2,427,000	2,796,000
Ending Balance: Individually evaluated for impairment	347,000	112,000	162,000
Ending Balance: Collectively evaluated for impairment	2,680,000	2,315,000	2,634,000
Ending Balance: Individually evaluated for impairment	895,000	491,000	442,000
Ending Balance: Collectively evaluated for impairment	323,074,000	320,151,000	327,321,000
Total Loans Outstanding	323,969,000	320,642,000	327,763,000
Consumer
Activity in ALL:
Beginning balance	234,000	233,000	233,000
Loans charged off	(14,000)	(26,000)	(96,000)
Recoveries	7,000	3,000	11,000
Provision (credit)(1)	32,000	20,000	86,000
Ending balance	259,000	230,000	234,000
Ending Balance: Individually evaluated for impairment	0	0
Ending Balance: Collectively evaluated for impairment	259,000	230,000	234,000
Ending Balance: Individually evaluated for impairment	0	0	6,000
Ending Balance: Collectively evaluated for impairment	20,733,000	18,011,000	20,618,000
Total Loans Outstanding	20,733,000	18,011,000	20,624,000
HPFC Portfolio Segment
Activity in ALL:
Beginning balance	337,000	451,000	451,000
Loans charged off	0	0	(255,000)
Recoveries	0	0	1,000
Provision (credit)(1)	(29,000)	(27,000)	140,000
Ending balance	308,000	424,000	337,000
Ending Balance: Individually evaluated for impairment	0	0
Ending Balance: Collectively evaluated for impairment	308,000	424,000	337,000
Ending Balance: Individually evaluated for impairment	0	0
Ending Balance: Collectively evaluated for impairment	30,842,000	42,414,000	33,656,000
Total Loans Outstanding	$ 30,842,000	$ 42,414,000	$ 33,656,000