Loans (Narrative) (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
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	$ 33,264,043	$ 32,079,073	$ 32,135,555
Net deferred loan fees and costs and fair value accounting adjustments	13,100	(3,200)	(42,300)
Net deferred loan fees and costs and fair value accounting adjustments, paid by SBA under PPP	24,800
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	11,187,972	11,955,967	12,276,999
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	124,000	113,100	108,500
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	$ 1,081,988	$ 2,715,921	$ 3,379,013