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, 2017		Mar. 31, 2016		Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Reserve for unfunded commitments		$ 9,000		$ 24,000		$ 11,000
Activity in ALL:
Beginning balance		23,116,000		21,166,000		21,166,000
Loans charged off		(159,000)		(801,000)
Recoveries		183,000		104,000
Provision (credit)(1)		581,000	[1]	870,000	[1]	5,269,000
Ending balance		23,721,000		21,339,000		23,116,000
Ending Balance: Individually evaluated for impairment		1,734,000		1,280,000
Ending Balance: Collectively evaluated for impairment		21,987,000		20,059,000
Ending Balance: Individually evaluated for impairment		20,128,000		13,881,000
Ending Balance: Collectively evaluated for impairment		2,625,011,000		2,478,753,000
Total Loans Outstanding		2,645,139,000		2,492,634,000		2,594,564,000
Residential Real Estate
Activity in ALL:
Beginning balance		4,160,000		4,545,000		4,545,000
Loans charged off		(5,000)		(210,000)		(356,000)
Recoveries		0		40,000		95,000
Provision (credit)(1)		116,000		141,000		(124,000)	[1]
Ending balance		4,271,000		4,516,000		4,160,000
Ending Balance: Individually evaluated for impairment		485,000		512,000		483,000
Ending Balance: Collectively evaluated for impairment		3,786,000		4,004,000		3,677,000
Ending Balance: Individually evaluated for impairment		4,408,000		6,033,000		4,348,000
Ending Balance: Collectively evaluated for impairment		815,231,000		805,941,000		798,146,000
Total Loans Outstanding		819,639,000		811,974,000		802,494,000
Commercial Real Estate
Activity in ALL:
Beginning balance		12,154,000		10,432,000		10,432,000
Loans charged off		(3,000)		(222,000)		(315,000)
Recoveries		103,000		9,000		50,000
Provision (credit)(1)		472,000		161,000		1,987,000	[1]
Ending balance		12,726,000		10,380,000		12,154,000
Ending Balance: Individually evaluated for impairment		1,100,000		158,000		1,373,000
Ending Balance: Collectively evaluated for impairment		11,626,000		10,222,000		10,781,000
Ending Balance: Individually evaluated for impairment		13,191,000		3,130,000		13,317,000
Ending Balance: Collectively evaluated for impairment		1,083,284,000		949,351,000		1,037,463,000
Total Loans Outstanding		1,096,475,000		952,481,000		1,050,780,000
Commercial
Activity in ALL:
Beginning balance		3,755,000		3,241,000		3,241,000
Loans charged off		(136,000)		(226,000)		(2,218,000)
Recoveries		77,000		52,000		332,000
Provision (credit)(1)		119,000		231,000		2,400,000	[1]
Ending balance		3,815,000		3,298,000		3,755,000
Ending Balance: Individually evaluated for impairment		0		214,000
Ending Balance: Collectively evaluated for impairment		3,815,000		3,084,000		3,755,000
Ending Balance: Individually evaluated for impairment		1,994,000		3,862,000		2,028,000
Ending Balance: Collectively evaluated for impairment		331,613,000		288,202,000		331,611,000
Total Loans Outstanding		333,607,000		292,064,000		333,639,000
Home Equity
Activity in ALL:
Beginning balance		2,194,000		2,731,000		2,731,000
Loans charged off		(1,000)		(128,000)		(308,000)
Recoveries		1,000		1,000		2,000
Provision (credit)(1)		(87,000)		18,000		(231,000)	[1]
Ending balance		2,107,000		2,622,000		2,194,000
Ending Balance: Individually evaluated for impairment		83,000		89,000		86,000
Ending Balance: Collectively evaluated for impairment		2,024,000		2,533,000		2,108,000
Ending Balance: Individually evaluated for impairment		430,000		492,000		457,000
Ending Balance: Collectively evaluated for impairment		322,396,000		344,005,000		329,450,000
Total Loans Outstanding		322,826,000		344,497,000		329,907,000
Consumer
Activity in ALL:
Beginning balance		181,000		193,000		193,000
Loans charged off		(14,000)		(15,000)		(101,000)
Recoveries		2,000		2,000		7,000
Provision (credit)(1)		6,000		2,000		82,000	[1]
Ending balance		175,000		182,000		181,000
Ending Balance: Individually evaluated for impairment		0		0
Ending Balance: Collectively evaluated for impairment		175,000		182,000		181,000
Ending Balance: Individually evaluated for impairment		7,000		7,000		7,000
Ending Balance: Collectively evaluated for impairment		16,662,000		17,182,000		17,325,000
Total Loans Outstanding		16,669,000		17,189,000		17,332,000
HPFC Portfolio Segment
Activity in ALL:
Beginning balance		672,000		24,000		24,000
Loans charged off		0		0		(507,000)
Recoveries		0		0
Provision (credit)(1)		(45,000)		317,000		1,155,000	[1]
Ending balance		627,000		341,000		672,000
Ending Balance: Individually evaluated for impairment		66,000		307,000		65,000
Ending Balance: Collectively evaluated for impairment		561,000		34,000		607,000
Ending Balance: Individually evaluated for impairment		98,000		357,000		97,000
Ending Balance: Collectively evaluated for impairment		55,825,000		74,072,000		60,315,000
Total Loans Outstanding		55,923,000		74,429,000		60,412,000
Unallocated
Activity in ALL:
Beginning balance		$ 23,116,000		$ 21,166,000		21,166,000
Loans charged off						(3,805,000)
Recoveries						486,000
Provision (credit)(1)	[1]					5,269,000
Ending balance						23,116,000
Ending Balance: Individually evaluated for impairment						2,007,000
Ending Balance: Collectively evaluated for impairment						21,109,000
Ending Balance: Individually evaluated for impairment						20,254,000
Ending Balance: Collectively evaluated for impairment						2,574,310,000
Total Loans Outstanding						$ 2,594,564,000

[1] (1) The provision (credit) for loan losses excludes any impact for the change in the reserve for unfunded commitments, which represents management's estimate of the amount required to reflect the probable inherent losses on outstanding letters of credit and unused lines of credit. The reserve for unfunded commitments is presented within accrued interest and other liabilities on the consolidated statements of condition. At March 31, 2017 and 2016, and December 31, 2016, the reserve for unfunded commitments was $9,000, $24,000 and $11,000, respectively.