Loans and Leases (Narrative) (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022 USD ($) loan	Jun. 30, 2021 USD ($) loan	Jun. 30, 2022 USD ($) loan	Jun. 30, 2021 USD ($) loan	Jan. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase in loans and leases			$ 23,400,000
Loans and leases purchase discount	$ 317,600		317,600
Unamortized premiums	(103,700)		(103,700)			$ 12,300
Interest receivable	140,200		140,200			50,700
Interest on non-accrual loans	$ 5,200	$ 2,900	$ 8,600	$ 6,100
Loans and leases modified as TDRs within previous 12 months for which there was a payment default | loan	0	0	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	$ 1,000	$ 300	$ 10,000	$ 1,900
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Write-down	100	$ 0	100	$ 300
Collateral Pledged | FHLB
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged as collateral	8,300,000		8,300,000
Collateral Pledged | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired financing receivable	52,200		52,200			16,600
Collateral Pledged | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired financing receivable	17,400		17,400			34,900
Collateral Value
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired financing receivable	$ 115,300		$ 115,300			$ 86,000