FAIR VALUE MEASUREMENTS - Schedule of Additional Information about Assets Measured at Fair Value on Non-Recurring Basis (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	$ 0.0	$ 0.0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	0.0	0.0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	73.0	71.0
Mortgage Servicing Rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	71.8	68.6	$ 46.0	$ 35.6
SBA-Guaranteed Loan Servicing
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	1.0	2.0	$ 3.0
Fair value, measurements, nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent loans	35.0	34.0
Indirect installment loans held for sale	338.3
Other real estate owned	2.0	3.0
Fair value, measurements, nonrecurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent loans	0.0	0.0
Indirect installment loans held for sale	0.0
Other real estate owned	0.0	0.0
Fair value, measurements, nonrecurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent loans	0.0	0.0
Indirect installment loans held for sale	0.0
Other real estate owned	0.0	0.0
Fair value, measurements, nonrecurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent loans	35.0	34.0
Indirect installment loans held for sale	338.0
Other real estate owned	2.0	3.0
Fair value, measurements, nonrecurring | Mortgage Servicing Rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	12.0
Fair value, measurements, nonrecurring | Mortgage Servicing Rights | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	0.0
Fair value, measurements, nonrecurring | Mortgage Servicing Rights | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	0.0
Fair value, measurements, nonrecurring | Mortgage Servicing Rights | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	12.0
Fair value, measurements, nonrecurring | SBA-Guaranteed Loan Servicing
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	1.0	2.0
Fair value, measurements, nonrecurring | SBA-Guaranteed Loan Servicing | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	0.0	0.0
Fair value, measurements, nonrecurring | SBA-Guaranteed Loan Servicing | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	0.0	0.0
Fair value, measurements, nonrecurring | SBA-Guaranteed Loan Servicing | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	$ 1.0	$ 2.0