Derivative Financial Instruments - Additional information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Derivative [Line Items]
Credit exposure to settled variation margin in excess of customer related interest rate swap (less than)	$ 1.4		$ 0.4
Derivative, gain (loss) on derivative, net	(0.2)	$ (0.2)
Loan Origination Commitments
Derivative [Line Items]
Derivative, notional amount	22.8		31.9
Derivative asset	0.2		0.3
Derivative liability	0.2		0.1
Forward Contracts
Derivative [Line Items]
Derivative, notional amount	12.9		24.4
Non Cleared Derivative Transactions | Customer Related Interest Rate Swap Derivatives
Derivative [Line Items]
Fair value of interest rate swap liabilities that are net in a net liability position	0.2		13.7
Cash and Cash Equivalents | Non Cleared Derivative Transactions | Customer Related Interest Rate Swap Derivatives
Derivative [Line Items]
Additional collateral posted	5.5
Available-for-sale Securities | Non Cleared Derivative Transactions | Customer Related Interest Rate Swap Derivatives
Derivative [Line Items]
Additional collateral posted			21.3
Restricted Assets | Cash and Cash Equivalents | Cleared Derivative Transaction
Derivative [Line Items]
Additional collateral posted	37.0
Restricted Assets | Available-for-sale Securities | Cleared Derivative Transaction
Derivative [Line Items]
Additional collateral posted			$ 48.9
Interest Income | Termination Of Cash Flow Hedges
Derivative [Line Items]
Interest rate swap cash flow hedges amount expected to reclassified from other comprehensive income to income statement in the next twelve months	$ 4.9