Loans and Leases and the Allowance for Credit Losses - Changes in Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 1,019,671	$ 1,001,430	$ 1,017,198	$ 988,997
Provision for credit losses	35,000	52,000	78,000	107,000
Net charge-offs
Charge-offs	(57,447)	(61,682)	(114,199)	(124,246)
Recoveries	22,024	16,477	38,249	36,474
Net charge-offs	(35,423)	(45,205)	(75,950)	(87,772)
Ending balance	1,019,248	1,008,225	1,019,248	1,008,225
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	326,071	347,760	328,599	330,833
Provision for credit losses	11,250	13,368	18,480	42,191
Net charge-offs
Charge-offs	(14,900)	(25,247)	(29,481)	(41,604)
Recoveries	6,409	3,433	11,232	7,894
Net charge-offs	(8,491)	(21,814)	(18,249)	(33,710)
Ending balance	328,830	339,314	328,830	339,314
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	367,717	360,010	374,085	362,719
Provision for credit losses	(10,845)	7,638	(16,070)	8,900
Net charge-offs
Charge-offs	(4,548)	(1,853)	(5,914)	(7,298)
Recoveries	1,437	434	1,660	1,908
Net charge-offs	(3,111)	(1,419)	(4,254)	(5,390)
Ending balance	353,761	366,229	353,761	366,229
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	73,047	62,012	65,405	61,127
Provision for credit losses	5,242	7,163	15,728	12,800
Net charge-offs
Charge-offs	(3,966)	(5,899)	(8,320)	(12,158)
Recoveries	1,800	2,730	3,310	4,237
Net charge-offs	(2,166)	(3,169)	(5,010)	(7,921)
Ending balance	76,123	66,006	76,123	66,006
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	173,841	153,172	170,809	156,288
Provision for credit losses	30,801	24,190	60,615	43,022
Net charge-offs
Charge-offs	(34,033)	(28,683)	(70,484)	(63,186)
Recoveries	12,378	9,880	22,047	22,435
Net charge-offs	(21,655)	(18,803)	(48,437)	(40,751)
Ending balance	182,987	158,559	182,987	158,559
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	78,995	78,476	78,300	78,030
Provision for credit losses	(1,448)	(359)	(753)	87
Net charge-offs
Ending balance	$ 77,547	$ 78,117	$ 77,547	$ 78,117