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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 1,019,337	$ 1,019,671	$ 1,019,444	$ 1,017,198
Provision for credit losses	55,000	35,000	77,000	78,000
Net charge-offs
Charge-offs	(69,406)	(57,447)	(114,506)	(114,199)
Recoveries	24,936	22,024	47,929	38,249
Net charge-offs	(44,470)	(35,423)	(66,577)	(75,950)
Ending balance	1,029,867	1,019,248	1,029,867	1,019,248
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	335,620	326,071	330,055	328,599
Provision for credit losses	10,337	11,250	16,608	18,480
Net charge-offs
Charge-offs	(16,608)	(14,900)	(25,108)	(29,481)
Recoveries	6,506	6,409	14,300	11,232
Net charge-offs	(10,102)	(8,491)	(10,808)	(18,249)
Ending balance	335,855	328,830	335,855	328,830
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	337,995	367,717	341,655	374,085
Provision for credit losses	14,501	(10,845)	10,298	(16,070)
Net charge-offs
Charge-offs	(10,165)	(4,548)	(10,448)	(5,914)
Recoveries	965	1,437	1,791	1,660
Net charge-offs	(9,200)	(3,111)	(8,657)	(4,254)
Ending balance	343,296	353,761	343,296	353,761
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	65,136	73,047	69,125	65,405
Provision for credit losses	(2,376)	5,242	(4,823)	15,728
Net charge-offs
Charge-offs	(3,263)	(3,966)	(6,635)	(8,320)
Recoveries	1,514	1,800	3,344	3,310
Net charge-offs	(1,749)	(2,166)	(3,291)	(5,010)
Ending balance	61,011	76,123	61,011	76,123
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	203,045	173,841	200,564	170,809
Provision for credit losses	31,594	30,801	54,477	60,615
Net charge-offs
Charge-offs	(39,370)	(34,033)	(72,315)	(70,484)
Recoveries	15,951	12,378	28,494	22,047
Net charge-offs	(23,419)	(21,655)	(43,821)	(48,437)
Ending balance	211,220	182,987	211,220	182,987
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	77,541	78,995	78,045	78,300
Provision for credit losses	944	(1,448)	440	(753)
Net charge-offs
Ending balance	$ 78,485	$ 77,547	$ 78,485	$ 77,547