RELATED PARTY TRANSACTIONS (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Loans to Related Parties [Roll Forward]
Balance at beginning of year	$ 59,973,000	$ 62,741,000
New loans or additional advances	7,461,000	1,895,000
Effect of changes in composition of related parties	0	4,456,000
Repayments	(11,382,000)	(9,119,000)
Balance at end of year	56,052,000	59,973,000	$ 62,741,000
Deposit liabilities	39,500,000	18,300,000
Rent expense	1,000,000.0	1,000,000.0
Rent expense			1,100,000
Legal accruals and settlements	0	0	989,000
Fee income	$ 59,089,000	58,245,000	57,840,000
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	$ 0	10,000	28,000
1365 New Scotland Road, Slingerlands, New York | Director
Loans to Related Parties [Roll Forward]
Monthly rent expense	4,000
Rent expense	51,000	52,000
Rent expense			45,000
2 Rush Street, Schenectady, New York | Director
Loans to Related Parties [Roll Forward]
Monthly rent expense	8,000
Rent expense	106,000	93,000
Rent expense			84,000
127 Court Street, Binghamton, New York | Director
Loans to Related Parties [Roll Forward]
Monthly rent expense	$ 5,000
Related party, ownership percentage	20.00%
Participating mortgage loans, income from insurance products (less than $1 thousand)			1,000
Participating mortgage loans, purchase of insurance product			34,000
WMG | Operating Segments | Trust Services | Management
Loans to Related Parties [Roll Forward]
Fee income	$ 614,000	$ 580,000	$ 593,000