Loans and Leases and the Allowance for Credit Losses - Summary of Outstanding Loan Balances Related to COVID-19 Modifications Granted - (Parenthetical) (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Financing Receivable Allowance For Credit Losses [Line Items]
Loans and leases, net of unearned discount		$ 129,961	$ 66,517
Payment Deferral [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans and leases, net of unearned discount		85,516	$ 13,019
C O V I D19
Financing Receivable Allowance For Credit Losses [Line Items]
Loans and leases, net of unearned discount		4,632,997
C O V I D19 | Payment Deferral [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans and leases, net of unearned discount	[1]	4,013,941
C O V I D19 | Payment Deferral [Member] | Government-Guaranteed Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans and leases, net of unearned discount		$ 2,400,000

[1] Represents accruing loans at March 31, 2021 for which a COVID-19 related payment deferral (including maturity extensions) has been granted