Loans and Allowance for Credit Losses - Additional Information (Details)			3 Months Ended		9 Months Ended
		Sep. 30, 2023 USD ($) loan	Sep. 30, 2023 USD ($) loan	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) loan	Sep. 30, 2022 USD ($)	Jun. 30, 2023 USD ($)	Dec. 31, 2022 USD ($) loan	Jun. 30, 2022 USD ($)	Jan. 01, 2022 USD ($)	Dec. 31, 2021 USD ($)
Changes in lines of credit,resrticted to commercial exposure
Loan syndications, amount		$ 100,000,000	$ 100,000,000		$ 100,000,000
Financing receivable, excluding accrued interest, after allowance for credit loss		13,744,822,000	13,744,822,000		13,744,822,000			$ 13,420,317,000
Debt, long-term and short-term, combined amount		715,372,000	715,372,000		715,372,000			740,828,000
Mortgage loans partially or wholly-owned by others and serviced by the Company		78,800,000	78,800,000		78,800,000			84,000,000
Loan purchases			0	$ 79,900,000	32,000,000	$ 79,900,000
Proceeds from sales of commercial loans					189,296,000	0
Realized loss on sales of commercial loans	[1]				(2,505,000)	0
Financing receivable, allowance for credit loss, excluding accrued interest		155,146,000	155,146,000	131,663,000	$ 155,146,000	131,663,000	$ 147,955,000	142,211,000	$ 125,531,000		$ 97,787,000
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
Amounts charged-off on TDRs						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		4,200,000,000	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			1,100,000,000
Residential Real Estate
Changes in lines of credit,resrticted to commercial exposure
Financing receivable, collateral dependent loans		900,000	900,000		900,000			600,000
Commercial Portfolio Segment
Changes in lines of credit,resrticted to commercial exposure
Financing receivable, collateral dependent loans		27,800,000	27,800,000		27,800,000			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		14,900,000	14,900,000		14,900,000			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 | Residential Real Estate
Changes in lines of credit,resrticted to commercial exposure
Amortized cost of loans purchased		391,700,000	391,700,000		391,700,000			376,100,000
Financing receivable, allowance for credit loss, excluding accrued interest		$ 26,355,000	$ 26,355,000	23,007,000	$ 26,355,000	23,007,000	27,012,000	$ 28,129,000	21,663,000		6,556,000
Number of loans in process of foreclosure | loan		1	1		1			0
Mortgage loans in process of foreclosure, amount		$ 100,000	$ 100,000		$ 100,000
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
Consumer home equity | Consumer Portfolio Segment
Changes in lines of credit,resrticted to commercial exposure
Financing receivable, allowance for credit loss, excluding accrued interest		$ 5,482,000	$ 5,482,000	5,842,000	$ 5,482,000	5,842,000	6,044,000	$ 6,454,000	5,662,000		3,722,000
Number of loans in process of foreclosure | loan		3	3		3			0
Mortgage loans in process of foreclosure, amount		$ 400,000	$ 400,000		$ 400,000
Consumer home equity | Cumulative effect accounting adjustment | Consumer Portfolio Segment
Changes in lines of credit,resrticted to commercial exposure
Financing receivable, allowance for credit loss, excluding accrued interest								$ (201,000)			1,857,000
Commercial and industrial | Commercial Portfolio Segment
Changes in lines of credit,resrticted to commercial exposure
Proceeds from sales of commercial loans			191,800,000		191,800,000
Realized loss on sales of commercial loans			$ 2,500,000		$ 2,500,000
Number of loans transferred to held-for-sale | loan		1	1		1
Financing receivable, transfer to held-for-sale		$ 22,400,000
Transfer to held-for-sale, loss		200,000
Financing receivable, allowance for credit loss, excluding accrued interest		26,518,000	$ 26,518,000	$ 26,841,000	$ 26,518,000	$ 26,841,000	$ 29,535,000	26,859,000	$ 25,852,000		18,018,000
Commercial and industrial | Cumulative effect accounting adjustment | Commercial Portfolio Segment
Changes in lines of credit,resrticted to commercial exposure
Financing receivable, allowance for credit loss, excluding accrued interest								47,000			$ 11,533,000
Federal Home Loan Bank Advances
Changes in lines of credit,resrticted to commercial exposure
Advance from Federal Home Loan Bank		673,500,000	673,500,000		673,500,000			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			$ 0
Unrated | Minimum
Changes in lines of credit,resrticted to commercial exposure
Lines of credit, exposure		100,000	100,000		100,000
Unrated | Line of Credit | Commercial Portfolio Segment | Maximum
Changes in lines of credit,resrticted to commercial exposure
Lines of credit, exposure		1,500,000	1,500,000		1,500,000
Unrated | Line of Credit | Business Banking | Commercial Portfolio Segment | Maximum
Changes in lines of credit,resrticted to commercial exposure
Lines of credit, exposure		$ 1,500,000	$ 1,500,000		$ 1,500,000

[1] Excludes the mark-to-market adjustment related to one commercial and industrial loan transferred to held for sale during the nine months ended September 30, 2023 which is included in the change in loans held for sale.