RELATED PARTY TRANSACTIONS (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Loans to Related Parties [Roll Forward]
Balance at beginning of year	$ 35,469,000	$ 36,911,000
New loans or additional advances	6,872,000	5,742,000
Repayments	(3,188,000)	(7,184,000)
Balance at end of year	39,153,000	35,469,000	$ 36,911,000
Deposit liabilities	11,300,000	10,300,000
Legal accruals and settlements	850,000	1,200,000	0
Fee income	$ 52,840,000	49,677,000	48,271,000
Minimum
Related Party Transactions [Line Items]
Related party principal ownership threshold (in hundredths)	10.00%
Director
Loans to Related Parties [Roll Forward]
Legal accruals and settlements	$ 17,000	36,000	88,000
7 Southside Drive, Clifton Park, New York | Director
Loans to Related Parties [Roll Forward]
Monthly rent expense	4,000
25 Park Avenue, Clifton Park, New York | Director
Loans to Related Parties [Roll Forward]
Monthly rent expense	11,000
1365 New Scotland Road, Slingerlands, New York | Director
Loans to Related Parties [Roll Forward]
Monthly rent expense	4,000
Rent expense	51,000	169,000	90,000
127 Court Street, Binghamton, New York | Director
Loans to Related Parties [Roll Forward]
Monthly rent expense	$ 5,000
Related party, ownership percentage	20.00%
Rent expense	$ 79,000	62,000
Participating mortgage loans, amount sold	2,000,000	1,900,000	0
Participating mortgage loans, participation liabilities, amount	6,600,000	4,700,000
Participating mortgage loans, income(loss) From Insurance Products	1,000	2,000	0
Participating Mortgage Loans, Purchase Of Insurance Product	34,000	0	0
WMG | Operating Segments | Trust Services | Management
Loans to Related Parties [Roll Forward]
Fee income	$ 332,000	$ 328,000	$ 904,000