RELATED PARTY TRANSACTIONS (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Loans to Related Parties [Roll Forward]
Balance at beginning of year	$ 39,153,000	$ 35,469,000
New loans or additional advances	10,624,000	6,872,000
Effect of changes in composition of related parties	25,815,000	0
Repayments	(12,851,000)	(3,188,000)
Balance at end of year	62,741,000	39,153,000	$ 35,469,000
Deposit liabilities	22,200,000	11,300,000
Legal accruals and settlements	989,000	850,000	1,200,000
Fee income	$ 57,840,000	52,840,000	49,677,000
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	$ 28,000	17,000	36,000
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	45,000	51,000	169,000
127 Court Street, Binghamton, New York | Director
Loans to Related Parties [Roll Forward]
Monthly rent expense	$ 5,000
Rent expense		79,000	62,000
Related party, ownership percentage	20.00%
Participating mortgage loans, amount sold		2,000,000	1,900,000
Participating mortgage loans, participation liabilities, amount		6,600,000	4,700,000
Participating mortgage loans, income from insurance products (less than $1 thousand)		1,000	2,000
Participating mortgage loans, purchase of insurance product		34,000		$ 0
WMG | Operating Segments | Trust Services | Management
Loans to Related Parties [Roll Forward]
Fee income	$ 593,000	$ 332,000	$ 328,000