LOANS AND LEASES - Additional Information (Detail) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2021 USD ($) State	Dec. 31, 2020 USD ($)	Mar. 31, 2021 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrued interest receivable	$ 56.9	$ 62.9
Purchased with credit deterioration included with allowance for credit losses, amount	50.3
Purchased with credit deterioration, discount	110.0
Discount remaining	$ 39.3	50.9
Number of states, company operating financial services | State	7
Loans granted short-term modification due to COVID-19	$ 170.0
Restructured loans returned to performing status	6.9
Total loan on allowance	357.0	363.0	$ 362.0
Pooled reserves for all other classes of loans	$ 3.7	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]
Guaranteed percentage	100.00%
Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value of OREO through foreclosure	$ 1.3	2.5
Mortgage loans on real estate, foreclosure	5.7	8.2
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loan on allowance	81.0	81.0	79.0	$ 98.0	$ 88.0	$ 53.0
Commercial and Industrial [Member] | Paycheck Protection Program Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans to customers	1,600.0	2,200.0
Commercial Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, collateral dependent	54.0
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	274.0	280.0	$ 281.0	$ 279.0	$ 254.0	$ 133.0
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	1.4	2.8
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	$ 2.3	$ 2.5