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, 2020	Mar. 31, 2019	Dec. 31, 2019
Financing Receivable, Allowance for Credit Losses [Line Items]
Reserve for unfunded commitments	$ 24,000	$ 16,000	$ 21,000
Activity in ALL:
Beginning balance	25,171,000	24,712,000	24,712,000
Loans charged off	(490,000)	(336,000)	(2,713,000)
Recoveries	68,000	75,000	310,000
Provision (credit)(1)	1,772,000	750,000	2,862,000
Ending balance	26,521,000	25,201,000	25,171,000
Ending Balance: Individually evaluated for impairment	447,000	927,000	463,000
Ending Balance: Collectively evaluated for impairment	26,074,000	24,274,000	24,708,000
Ending Balance: Individually evaluated for impairment	4,355,000	6,264,000	4,478,000
Ending Balance: Collectively evaluated for impairment	3,153,407,000	3,036,178,000	3,090,545,000
Total Loans Outstanding	3,157,762,000	3,042,442,000	3,095,023,000
Residential Real Estate
Activity in ALL:
Beginning balance	5,842,000	6,071,000	6,071,000
Loans charged off	(96,000)	(11,000)	(462,000)
Recoveries	2,000	2,000	16,000
Provision (credit)(1)	149,000	91,000	217,000
Ending balance	5,897,000	6,153,000	5,842,000
Ending Balance: Individually evaluated for impairment	324,000	553,000	364,000
Ending Balance: Collectively evaluated for impairment	5,573,000	5,600,000	5,478,000
Ending Balance: Individually evaluated for impairment	3,286,000	4,736,000	3,384,000
Ending Balance: Collectively evaluated for impairment	1,060,926,000	1,012,706,000	1,066,990,000
Total Loans Outstanding	1,064,212,000	1,017,442,000	1,070,374,000
Commercial Real Estate
Activity in ALL:
Beginning balance	12,414,000	11,654,000	11,654,000
Loans charged off	(50,000)	(65,000)	(300,000)
Recoveries	4,000	4,000	49,000
Provision (credit)(1)	1,006,000	245,000	1,011,000
Ending balance	13,374,000	11,838,000	12,414,000
Ending Balance: Individually evaluated for impairment	34,000	27,000	30,000
Ending Balance: Collectively evaluated for impairment	13,340,000	11,811,000	12,384,000
Ending Balance: Individually evaluated for impairment	400,000	410,000	402,000
Ending Balance: Collectively evaluated for impairment	1,299,460,000	1,258,064,000	1,242,995,000
Total Loans Outstanding	1,299,860,000	1,258,474,000	1,243,397,000
Commercial
Activity in ALL:
Beginning balance	3,769,000	3,620,000	3,620,000
Loans charged off	(253,000)	(236,000)	(1,167,000)
Recoveries	53,000	62,000	225,000
Provision (credit)(1)	545,000	170,000	1,091,000
Ending balance	4,114,000	3,616,000	3,769,000
Ending Balance: Individually evaluated for impairment	0	0
Ending Balance: Collectively evaluated for impairment	4,114,000	3,616,000	3,769,000
Ending Balance: Individually evaluated for impairment	299,000	223,000	319,000
Ending Balance: Collectively evaluated for impairment	444,531,000	390,759,000	420,789,000
Total Loans Outstanding	444,830,000	390,982,000	421,108,000
Home Equity
Activity in ALL:
Beginning balance	2,423,000	2,796,000	2,796,000
Loans charged off	(34,000)	(10,000)	(412,000)
Recoveries	4,000	0	1,000
Provision (credit)(1)	87,000	241,000	38,000
Ending balance	2,480,000	3,027,000	2,423,000
Ending Balance: Individually evaluated for impairment	89,000	347,000	69,000
Ending Balance: Collectively evaluated for impairment	2,391,000	2,680,000	2,354,000
Ending Balance: Individually evaluated for impairment	370,000	895,000	373,000
Ending Balance: Collectively evaluated for impairment	305,856,000	323,074,000	312,406,000
Total Loans Outstanding	306,226,000	323,969,000	312,779,000
Consumer
Activity in ALL:
Beginning balance	507,000	234,000	234,000
Loans charged off	(57,000)	(14,000)	(301,000)
Recoveries	5,000	7,000	19,000
Provision (credit)(1)	18,000	32,000	555,000
Ending balance	473,000	259,000	507,000
Ending Balance: Individually evaluated for impairment	0	0
Ending Balance: Collectively evaluated for impairment	473,000	259,000	507,000
Ending Balance: Individually evaluated for impairment	0	0
Ending Balance: Collectively evaluated for impairment	24,377,000	20,733,000	25,772,000
Total Loans Outstanding	24,377,000	20,733,000	25,772,000
HPFC Portfolio Segment
Activity in ALL:
Beginning balance	216,000	337,000	337,000
Loans charged off	0	0	(71,000)
Recoveries	0	0
Provision (credit)(1)	(33,000)	(29,000)	(50,000)
Ending balance	183,000	308,000	216,000
Ending Balance: Individually evaluated for impairment	0	0
Ending Balance: Collectively evaluated for impairment	183,000	308,000	216,000
Ending Balance: Individually evaluated for impairment	0	0
Ending Balance: Collectively evaluated for impairment	18,257,000	30,842,000	21,593,000
Total Loans Outstanding	$ 18,257,000	$ 30,842,000	$ 21,593,000