Other Real Estate Owned (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Repossessed Assets [Abstract]
Balance at beginning of year	$ 14.4	$ 16.8	$ 12.7	$ 2.0
OREO acquired through acquisitions	0.0	0.0	0.0	15.8
Additions	0.0	0.3	2.5	0.4
Write-down of OREO	(0.3)	(0.2)	(1.1)	(0.2)
Dispositions	(2.5)	(0.5)	(2.5)	(1.6)
Balance at end of year	$ 11.6	$ 16.4	$ 11.6	$ 16.4