ALLOWANCE FOR LOAN AND LEASE LOSSES AND CREDIT QUALITY INFORMATION - Additional Information (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($) loan	Sep. 30, 2018 USD ($) loan	Sep. 30, 2019 USD ($) SecurityLoan loan	Sep. 30, 2018 USD ($) loan	Dec. 31, 2018 USD ($) SecurityLoan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs			$ 15,800,000	$ 8,700,000
Percentage of average loans annualized, charged-offs			0.27%	0.24%
Interest income on impaired loans	$ 200,000	$ 600,000	$ 600,000	$ 1,300,000
Troubled debt restructuring related reserves	$ 700,000		$ 700,000		$ 1,200,000
Usual sustained repayment performance period			6 months
TRD defaulted | loan	2	5	6	9
Subsequent default, loan amount	$ 200,000	$ 500,000	$ 1,500,000	$ 700,000
Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of residential loans in the process of foreclosure | SecurityLoan			40		26
Total loans outstanding, residential loans			$ 4,200,000		$ 1,900,000
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of residential loans in the process of foreclosure | SecurityLoan			32		11
Total loans outstanding, residential loans			$ 11,300,000		$ 5,300,000
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Period for impairment loans			90 days
Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in allowance for loan losses	100,000	100,000	$ 200,000	700,000
Troubled debt restructurings charged off	$ 0	$ 0	$ 0	$ 100,000
Total Residential and Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impairment loans, charge off period			90 days