Business Segment Reporting - Schedule of Segment Financial Results (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Net interest income		$ 173,941	$ 163,868
Provision for credit losses	[1]	88,000	12,350
Noninterest income		98,424	107,382
Noninterest expense		188,619	190,626
(Loss) income before income taxes		(4,254)	68,274
Income tax (benefit) expense		(815)	10,530
NET (LOSS) INCOME		(3,439)	57,744
Average assets		26,040,000	22,854,000
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net interest income		106,948	99,814
Provision for credit losses		82,220	10,329
Noninterest income		11,240	23,181
Noninterest expense		59,043	66,820
(Loss) income before income taxes		(23,075)	45,846
Income tax (benefit) expense		(4,421)	7,071
NET (LOSS) INCOME		(18,654)	38,775
Average assets		11,609,000	10,448,000
Institutional Banking [Member]
Segment Reporting Information [Line Items]
Net interest income		33,036	31,752
Provision for credit losses		275	286
Noninterest income		61,952	55,850
Noninterest expense		68,453	65,398
(Loss) income before income taxes		26,260	21,918
Income tax (benefit) expense		5,032	3,380
NET (LOSS) INCOME		21,228	18,538
Average assets		9,006,000	7,013,000
Personal Banking [Member]
Segment Reporting Information [Line Items]
Net interest income		33,957	32,302
Provision for credit losses		5,505	1,735
Noninterest income		25,232	28,351
Noninterest expense		61,123	58,408
(Loss) income before income taxes		(7,439)	510
Income tax (benefit) expense		(1,426)	79
NET (LOSS) INCOME		(6,013)	431
Average assets		$ 5,425,000	$ 5,393,000

[1] For the three months ended March 31, 2019, this line represents the Provision for loan losses. See further discussion of this change in Note 3, “New Accounting Pronouncements.