Other Operating Income - (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Components of Other Operating Income [Line Items]
Other operating income	$ 55.2	$ 45.6	$ 102.0	$ 86.7
Loan Service Fees
Components of Other Operating Income [Line Items]
Other operating income	21.4	18.1	40.1	34.8
Banking Service Fees
Components of Other Operating Income [Line Items]
Other operating income	13.6	12.9	25.8	25.6
Bank Owned Life Insurance
Components of Other Operating Income [Line Items]
Other operating income	17.0	14.9	33.7	26.7
Other Income
Components of Other Operating Income [Line Items]
Other operating income	$ 3.2	$ (0.3)	$ 2.4	$ (0.4)