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		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Financing Receivable Allowance For Credit Losses [Line Items]
Loans and leases, net of unearned discount		$ 124,785	$ 73,598	$ 507,582	$ 283,415
Payment Deferral [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans and leases, net of unearned discount		$ 56,116	$ 35,178	196,378	$ 117,336
COVID-19 [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans and leases, net of unearned discount				2,416,803
COVID-19 [Member] | Payment Deferral [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans and leases, net of unearned discount	[1]			2,115,790
COVID-19 [Member] | Payment Deferral [Member] | Government-Guaranteed Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans and leases, net of unearned discount				$ 1,600,000

[1] Represents accruing loans at September 30, 2021 for which a COVID-19 related payment deferral (including maturity extensions) has been granted