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Loans and Allowance for Credit Losses - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Jun. 30, 2022	Jan. 01, 2022	Dec. 31, 2021	Jun. 30, 2021	Dec. 31, 2020
Changes in lines of credit,resrticted to commercial exposure
Loan syndications, amount	$ 100,000,000		$ 100,000,000
Financing receivable, excluding accrued interest, after allowance for credit loss	12,752,942,000		12,752,942,000			$ 12,157,281,000
Mortgage loans partially or wholly-owned by others and serviced by the Company	85,700,000		85,700,000			95,800,000
Loan purchases	79,900,000		79,900,000
Financing receivable, allowance for credit loss, excluding accrued interest	131,663,000	$ 103,398,000	131,663,000	$ 125,531,000		97,787,000	$ 105,637,000	$ 113,031,000
Total loans	12,903,954,000		$ 12,903,954,000			12,281,510,000
Maximum number of days required for special mention			90 days
Amount of specific reserve associated with the TDR	1,800,000		$ 1,800,000			3,400,000
Amount of additional commitments to lend to borrowers who have been a party to a TDR	0		0			0
Outstanding recorded investment of loans that were new to troubled debt restructuring	9,200,000		9,200,000			800,000
Amounts charged-off on TDRs	0	$ 0
Federal Home Loan Bank Advances \| Asset Pledged as Collateral
Changes in lines of credit,resrticted to commercial exposure
Financing receivable, excluding accrued interest, after allowance for credit loss	3,300,000,000		3,300,000,000			2,600,000,000
Federal Reserve Bank Advances \| Asset Pledged as Collateral
Changes in lines of credit,resrticted to commercial exposure
Financing receivable, excluding accrued interest, after allowance for credit loss	1,100,000,000		1,100,000,000			784,000,000
Residential Real Estate
Changes in lines of credit,resrticted to commercial exposure
Financing receivable, collateral dependent loans	600,000		600,000			600,000
Commercial Portfolio Segment
Changes in lines of credit,resrticted to commercial exposure
Financing receivable, collateral dependent loans	12,800,000		12,800,000			13,100,000
Cumulative effect accounting adjustment
Changes in lines of credit,resrticted to commercial exposure
Financing receivable, allowance for credit loss, excluding accrued interest						27,086,000
CARES Act \| Payment Deferral
Changes in lines of credit,resrticted to commercial exposure
Loans which underwent a modification, CARES Act	17,700,000		17,700,000			106,700,000
Unfunded Loan Commitment
Changes in lines of credit,resrticted to commercial exposure
Financing receivable, allowance for credit loss, excluding accrued interest	11,400,000		11,400,000		$ 11,100,000
Unfunded Loan Commitment \| Cumulative effect accounting adjustment
Changes in lines of credit,resrticted to commercial exposure
Financing receivable, allowance for credit loss, excluding accrued interest					$ 1,000,000
Federal Home Loan Bank Advances
Changes in lines of credit,resrticted to commercial exposure
Advance from Federal Home Loan Bank	384,200,000		384,200,000			14,000,000
Federal Reserve Bank Advances
Changes in lines of credit,resrticted to commercial exposure
Debt, long-term and short-term, combined amount	0		0			0
Nonperforming Loans
Changes in lines of credit,resrticted to commercial exposure
Total loans						9,040,062,000
Unrated
Changes in lines of credit,resrticted to commercial exposure
Lines of credit, exposure	100,000		100,000
Unrated \| Nonperforming Loans
Changes in lines of credit,resrticted to commercial exposure
Total loans						872,544,000
Unrated \| Nonperforming Loans \| Paycheck Protection Program \| Commercial Portfolio Segment
Changes in lines of credit,resrticted to commercial exposure
Total loans	5,300,000		5,300,000			112,800,000
Unrated \| Nonperforming Loans \| Paycheck Protection Program \| Business Banking
Changes in lines of credit,resrticted to commercial exposure
Total loans	17,800,000		17,800,000			218,600,000
Unrated \| Line of Credit \| Commercial Portfolio Segment
Changes in lines of credit,resrticted to commercial exposure
Lines of credit, exposure	1,500,000		1,500,000
Unrated \| Line of Credit \| Business Banking
Changes in lines of credit,resrticted to commercial exposure
Lines of credit, exposure	$ 1,500,000		$ 1,500,000
Loss \| Nonperforming Loans
Changes in lines of credit,resrticted to commercial exposure
Total loans						$ 0