Loans and Leases (Narrative) (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($) loan	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($) loan	Jan. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase in loans and leases			$ 25,600,000
Loans and leases purchase discount	$ 317,600		317,600
Unamortized premiums	(83,400)		(83,400)			$ 12,300
Interest receivable	175,800		175,800			50,700
Interest on non-accrual loans	7,600	$ 2,400	14,100	$ 7,200
Aggregated amortized cost of loans and leases	900		900
Loans and leases modified as TDRs within previous 12 months for which there was a payment default | loan		0		0
Sterling
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases					$ 20,498,706
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Write-down	0	$ 1,100	10,000	$ 3,000
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Write-down	100	$ 0	200	$ 300
Collateral Pledged | FHLB | Asset Pledged as Collateral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged as collateral	10,000,000		10,000,000
Collateral Pledged | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired financing receivable	77,200		77,200			16,600
Collateral Pledged | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired financing receivable	46,300		46,300			34,900
Collateral Value
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired financing receivable	$ 147,900		$ 147,900			$ 86,000