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Investment recorded represented by troubled debt restructuring in the current period.

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Maximum exposure to credit risk of loans or receivables.

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Represents the aggregate of total long-term debt, including current maturities and short-term debt.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The aggregate amount of the participating mortgage obligation at the end of the accounting period.

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Loans and Allowance for Credit Losses - Additional Information (Detail) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2023	Jun. 30, 2022	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	Jan. 01, 2022	Dec. 31, 2021
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	13,798,721,000	13,798,721,000			$ 13,420,317,000
Debt, long-term and short-term, combined amount	351,211,000	351,211,000			740,828,000
Mortgage loans partially or wholly-owned by others and serviced by the Company	80,400,000	80,400,000			84,000,000
Loan purchases	0	32,000,000	$ 0
Financing receivable, allowance for credit loss, excluding accrued interest	147,955,000	147,955,000	125,531,000	$ 140,938,000	142,211,000	$ 124,166,000		$ 97,787,000
Total loans	13,961,878,000	$ 13,961,878,000			13,575,531,000
Maximum number of days required for special mention		90 days
Outstanding recorded investment of loans that were new to troubled debt restructuring					11,000,000
Amount of specific reserve associated with the TDR					1,800,000
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	4,200,000,000	$ 4,200,000,000			3,900,000,000
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			1,100,000,000
Residential Real Estate
Changes in lines of credit,resrticted to commercial exposure
Financing receivable, collateral dependent loans	400,000	400,000			600,000
Commercial Portfolio Segment
Changes in lines of credit,resrticted to commercial exposure
Financing receivable, collateral dependent loans	9,700,000	9,700,000			16,200,000
Cumulative effect accounting adjustment
Changes in lines of credit,resrticted to commercial exposure
Financing receivable, allowance for credit loss, excluding accrued interest					(1,143,000)			27,086,000
Unfunded Loan Commitment
Changes in lines of credit,resrticted to commercial exposure
Financing receivable, allowance for credit loss, excluding accrued interest	16,000,000	16,000,000			13,200,000		$ 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
Residential real estate
Changes in lines of credit,resrticted to commercial exposure
Financing receivable, allowance for credit loss, excluding accrued interest	27,012,000	27,012,000		$ 27,130,000
Residential real estate \| Residential Real Estate
Changes in lines of credit,resrticted to commercial exposure
Amortized cost of loans purchased	396,400,000	396,400,000			376,100,000
Financing receivable, allowance for credit loss, excluding accrued interest	27,012,000	27,012,000	$ 21,663,000		28,129,000	$ 22,243,000		6,556,000
Total loans	2,510,705,000	2,510,705,000			2,460,849,000
Residential real estate \| Cumulative effect accounting adjustment \| Residential Real Estate
Changes in lines of credit,resrticted to commercial exposure
Financing receivable, allowance for credit loss, excluding accrued interest					(849,000)			$ 13,489,000
Federal Home Loan Bank Advances
Changes in lines of credit,resrticted to commercial exposure
Advance from Federal Home Loan Bank	314,000,000	314,000,000			704,100,000
Federal Reserve Bank Advances
Changes in lines of credit,resrticted to commercial exposure
Debt, long-term and short-term, combined amount	0	0			$ 0
Unrated
Changes in lines of credit,resrticted to commercial exposure
Lines of credit, exposure	100,000	100,000
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