Loans and Leases and the Allowance for Credit Losses - Changes in Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 1,736,387	$ 1,051,071
Provision for credit losses	(25,000)	250,000
Net charge-offs
Charge-offs	(122,925)	(67,704)
Recoveries	47,744	18,542
Net (charge-offs) recoveries	(75,181)	(49,162)
Ending balance	1,636,206	1,384,366
Adoption of new accounting standard		132,457
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	405,846	366,094
Provision for credit losses	(72,418)	66,594
Net charge-offs
Charge-offs	(26,945)	(16,383)
Recoveries	22,511	3,261
Net (charge-offs) recoveries	(4,434)	(13,122)
Ending balance	328,994	358,092
Adoption of new accounting standard		(61,474)
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	670,719	322,201
Provision for credit losses	99,471	88,666
Net charge-offs
Charge-offs	(60,652)	(1,272)
Recoveries	6,560	438
Net (charge-offs) recoveries	(54,092)	(834)
Ending balance	716,098	433,689
Adoption of new accounting standard		23,656
One-to-Four Family Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	103,590	56,033
Provision for credit losses	(13,435)	9,291
Net charge-offs
Charge-offs	(2,399)	(5,102)
Recoveries	2,033	1,674
Net (charge-offs) recoveries	(366)	(3,428)
Ending balance	89,789	115,792
Adoption of new accounting standard		53,896
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance		77,625
Net charge-offs
Adoption of new accounting standard		(77,625)
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	556,232	229,118
Provision for credit losses	(38,618)	85,449
Net charge-offs
Charge-offs	(32,929)	(44,947)
Recoveries	16,640	13,169
Net (charge-offs) recoveries	(16,289)	(31,778)
Ending balance	$ 501,325	476,793
Adoption of new accounting standard		$ 194,004