Loans and Leases and the Allowance for Credit Losses - Changes in Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 1,017,198	$ 988,997
Provision for credit losses	43,000	55,000
Net charge-offs
Charge-offs	(56,752)	(62,564)
Recoveries	16,225	19,997
Net (charge-offs) recoveries	(40,527)	(42,567)
Ending balance	1,019,671	1,001,430
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	328,599	330,833
Provision for credit losses	7,230	28,823
Net charge-offs
Charge-offs	(14,581)	(16,357)
Recoveries	4,823	4,461
Net (charge-offs) recoveries	(9,758)	(11,896)
Ending balance	326,071	347,760
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	374,085	362,719
Provision for credit losses	(5,225)	1,262
Net charge-offs
Charge-offs	(1,366)	(5,445)
Recoveries	223	1,474
Net (charge-offs) recoveries	(1,143)	(3,971)
Ending balance	367,717	360,010
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	65,405	61,127
Provision for credit losses	10,486	5,637
Net charge-offs
Charge-offs	(4,354)	(6,259)
Recoveries	1,510	1,507
Net (charge-offs) recoveries	(2,844)	(4,752)
Ending balance	73,047	62,012
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	170,809	156,288
Provision for credit losses	29,814	18,832
Net charge-offs
Charge-offs	(36,451)	(34,503)
Recoveries	9,669	12,555
Net (charge-offs) recoveries	(26,782)	(21,948)
Ending balance	173,841	153,172
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	78,300	78,030
Provision for credit losses	695	446
Net charge-offs
Ending balance	$ 78,995	$ 78,476