ALLOWANCE FOR LOAN AND LEASE LOSSES AND CREDIT QUALITY INFORMATION - Additional Information (Details)	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2020 USD ($) loan	Mar. 31, 2020 SecurityLoan	Jun. 30, 2019 USD ($) loan	Jun. 30, 2020 USD ($) loan SecurityLoan	Jun. 30, 2019 USD ($) loan	Dec. 31, 2019 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	$ 200,000			$ 400,000
Interest income on impaired loans			$ 400,000		$ 600,000
Loan workout and other credit costs	4,587,000		1,419,000	5,040,000	1,690,000
Troubled debt restructuring related reserves	800,000			$ 800,000		$ 600,000
Usual sustained repayment performance period				6 months
Increase (decrease) in allowance for loan losses (less than)	100,000		100,000	$ 100,000	200,000
Troubled debt restructurings charged off	$ 0		$ 0	$ 0	$ 0
TRD defaulted | loan	0		3	0	4
Subsequent default, loan amount, less than			$ 1,200,000		$ 1,300,000
COVID-19
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified	$ 2,100,000,000
Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of residential loans in the process of foreclosure | SecurityLoan		33		25
Total loans outstanding, residential loans				$ 2,000,000.0		3,200,000
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of residential loans in the process of foreclosure | SecurityLoan		29		20
Total loans outstanding, residential loans				$ 6,200,000		$ 9,500,000
Residential and Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan workout and other credit costs	$ 1,100,000		$ 1,800,000	$ 1,100,000	$ 1,300,000
Impairment loans, charge off period				90 days