LOANS AND LEASES - Additional Information (Detail) - USD ($) $ in Millions			6 Months Ended	12 Months Ended
	Apr. 24, 2020	Jan. 01, 2020	Jun. 30, 2020	Dec. 31, 2019	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrued interest receivable			$ 65.6
Purchased with credit deterioration included with allowance for credit losses, amount		$ 50.3	50.3
Purchased with credit deterioration, discount			$ 110.0
Allocation balance	$ 349,000.0
Additional authorized amount	$ 320,000.0
Payment deferral period with forgiveness determination			10 months
Loans granted short-term modification due to COVID-19			$ 2,400.0
Restructured loans returned to performing status			6.1
Total loan on allowance		$ 196.0	365.0	$ 196.0	$ 343.0	$ 188.0	$ 186.0	$ 180.0
Pooled reserves for all other classes of loans			$ 5.0	4.1
Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Past due period for loan to be in default			90 days
Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Past due period for loan to be in default			12 months
SBA-Guaranteed Loan Servicing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fixed interest rate	1.00%
Term	2 years
Guaranteed percentage	100.00%
SBA-Guaranteed Loan Servicing [Member] | Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Processing fee paid by the SBA	1.00%
SBA-Guaranteed Loan Servicing [Member] | Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Processing fee paid by the SBA	5.00%
Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value of OREO through foreclosure			$ 2.9	3.3
Mortgage loans on real estate, foreclosure			0.1	9.2
Paycheck Protection Program Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans to custoemrs			2,500.0
Commercial Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, collateral dependent			73.0
Commercial Loan [Member] | Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Threshold for loans whose terms have been modified in a trouble debt restructuring, non accrual			1.0
Total Commercial Loans and Leases [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loan on allowance			279.0	133.0	$ 254.0
Total Commercial Loans and Leases [Member] | Specific and Pooled Reserves for Commercial Troubled Debt Restructurings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loan on allowance			1.0
Total Commercial Loans and Leases [Member] | Specific Reserves for Commercial Troubled Debt Restructurings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loan on allowance			1.6	1.6
Total Commercial Loans and Leases [Member] | Pooled Reserves For Commercial Troubled Debt Restructurings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loan on allowance			$ 3.4	$ 0.8