Loans and Leases and the Allowance for Credit Losses - Changes in Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 1,019,444	$ 1,017,198
Provision for credit losses	22,000	43,000
Net charge-offs
Charge-offs	(45,100)	(56,752)
Recoveries	22,993	16,225
Net (charge-offs) recoveries	(22,107)	(40,527)
Ending balance	1,019,337	1,019,671
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	330,055	328,599
Provision for credit losses	6,271	7,230
Net charge-offs
Charge-offs	(8,500)	(14,581)
Recoveries	7,794	4,823
Net (charge-offs) recoveries	(706)	(9,758)
Ending balance	335,620	326,071
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	341,655	374,085
Provision for credit losses	(4,203)	(5,225)
Net charge-offs
Charge-offs	(283)	(1,366)
Recoveries	826	223
Net (charge-offs) recoveries	543	(1,143)
Ending balance	337,995	367,717
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	69,125	65,405
Provision for credit losses	(2,447)	10,486
Net charge-offs
Charge-offs	(3,372)	(4,354)
Recoveries	1,830	1,510
Net (charge-offs) recoveries	(1,542)	(2,844)
Ending balance	65,136	73,047
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	200,564	170,809
Provision for credit losses	22,883	29,814
Net charge-offs
Charge-offs	(32,945)	(36,451)
Recoveries	12,543	9,669
Net (charge-offs) recoveries	(20,402)	(26,782)
Ending balance	203,045	173,841
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	78,045	78,300
Provision for credit losses	(504)	695
Net charge-offs
Ending balance	$ 77,541	$ 78,995