ALLOWANCE FOR CREDIT LOSSES AND CREDIT QUALITY INFORMATION - Analysis of Collateral Dependent and Impaired Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Property
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost basis of nonaccruing collateral-dependent loans	$ 23,239	$ 38,722
Equipment and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost basis of nonaccruing collateral-dependent loans	8,553	3,186
Commercial | Commercial and industrial | Property
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost basis of nonaccruing collateral-dependent loans	12,099	10,646
Commercial | Commercial and industrial | Equipment and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost basis of nonaccruing collateral-dependent loans	8,538	3,170
Commercial | Owner-occupied commercial | Property
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost basis of nonaccruing collateral-dependent loans	4,024	5,360
Commercial | Owner-occupied commercial | Equipment and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost basis of nonaccruing collateral-dependent loans	0	0
Commercial | Commercial mortgages | Property
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost basis of nonaccruing collateral-dependent loans	1,642	17,175
Commercial | Commercial mortgages | Equipment and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost basis of nonaccruing collateral-dependent loans	0	0
Commercial | Construction | Property
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost basis of nonaccruing collateral-dependent loans	0	0
Commercial | Construction | Equipment and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost basis of nonaccruing collateral-dependent loans	0	0
Residential | Property
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost basis of nonaccruing collateral-dependent loans	3,173	3,247
Residential | Equipment and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost basis of nonaccruing collateral-dependent loans	0	0
Consumer | Property
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost basis of nonaccruing collateral-dependent loans	2,301	2,294
Consumer | Equipment and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost basis of nonaccruing collateral-dependent loans	$ 15	$ 16