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		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Financing Receivable Allowance For Credit Losses [Line Items]
Loans and leases, net of unearned discount		$ 252,836	$ 143,300	$ 382,797	$ 209,817
Payment Deferral [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans and leases, net of unearned discount		$ 54,746	$ 69,139	140,262	$ 82,158
COVID-19 [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans and leases, net of unearned discount				3,140,313
COVID-19 [Member] | Payment Deferral [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans and leases, net of unearned discount	[1]			2,835,495
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				$ 2,000,000

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