Securities - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2021	Dec. 31, 2022
Schedule of Available-for-sale Securities [Line Items]
Realized gains on sales	$ 22.0	$ 9.3
Investments pledged, carrying value	255.8		$ 134.8
Investments pledged, carrying par value	30.0
Federal Reserve's Bank Term Funding Program [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments pledged, carrying value	61.7
Investments pledged, carrying par value	$ 69.9