Loans and Leases - Summary of Outstanding Loan Balances Related to COVID-19 Modifications Granted - (Parenthetical) (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable Allowance For Credit Losses [Line Items]
Loans and leases, net of unearned discount		$ 806,046	$ 127,024	$ 180,224
Payment Deferral [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans and leases, net of unearned discount		545,415	$ 29,481	$ 90,639
COVID-19 [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans and leases, net of unearned discount		4,579,759
COVID-19 [Member] | Payment Deferral [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans and leases, net of unearned discount	[1]	3,767,523
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		$ 1,700,000

[1] Represents accruing loans at December 31, 2020 for which a COVID-19 related payment deferral (including  maturity extensions) has been granted.