RELATED PARTY TRANSACTIONS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Loans to Related Parties [Roll Forward]
Balance at beginning of year	$ 62,741	$ 39,153
New loans or additional advances	1,895	10,624
Effect of changes in composition of related parties	4,456	25,815
Repayments	(9,119)	(12,851)
Balance at end of year	59,973	62,741	$ 39,153
Deposit liabilities	18,300	22,200
Rent expense	1,000
Legal accruals and settlements	0	989	850
Fee income	$ 58,245	57,840	52,840
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	$ 10	28	17
1365 New Scotland Road, Slingerlands, New York | Director
Loans to Related Parties [Roll Forward]
Monthly rent expense	4
Rent expense	52
Rent expense		45	51
2 Rush Street, Schenectady, New York | Director
Loans to Related Parties [Roll Forward]
Monthly rent expense	8
Rent expense	93
Rent expense		84
127 Court Street, Binghamton, New York | Director
Loans to Related Parties [Roll Forward]
Monthly rent expense	$ 5
Rent expense		79
Related party, ownership percentage	20.00%
Participating mortgage loans, amount sold		2,000
Participating mortgage loans, participation liabilities, amount		6,600
Participating mortgage loans, income from insurance products (less than $1 thousand)		1
Participating mortgage loans, purchase of insurance product		34	34
WMG | Operating Segments | Trust Services | Management
Loans to Related Parties [Roll Forward]
Fee income	$ 580	$ 593	$ 332