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Loans (Narrative) (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Schedule Of Accretable Yield Activity Related to Loans Acquired With Evidence Of Credit Quality Deterioration Since Origination Table [Line Items]
Net deferred loan fees and costs and fair value accounting adjustments	$ (42.3)	$ 9.1	$ 8.9
Net deferred loan fees and costs and fair value accounting adjustments, paid by SBA under PPP	49.3
Premium finance receivables
Schedule Of Accretable Yield Activity Related to Loans Acquired With Evidence Of Credit Quality Deterioration Since Origination Table [Line Items]
Unearned income portion of premium finance receivables	108.5	$ 118.4	$ 117.5
Commercial PPP Loans \| Commercial
Schedule Of Accretable Yield Activity Related to Loans Acquired With Evidence Of Credit Quality Deterioration Since Origination Table [Line Items]
Loans, net of unearned income	$ 3,400.0