Acquired and Covered Loans - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Certain Loans Acquired in Transfer Accounted for as Debt Securities Accretable Yield Movement Schedule [Line Items]
Non-residential mortgage loans with expired loss share agreements	$ 12.7	$ 14.9
Outstanding balance of PCI loans	210.7	84.8
Renewed non-purchased credit impaired loans	366.0	117.6
Acquired and Covered Receivables
Certain Loans Acquired in Transfer Accounted for as Debt Securities Accretable Yield Movement Schedule [Line Items]
Accretion on acquired loans	$ 33.9	$ 14.6	$ 16.3