Loans and Allowance for Credit Losses - Narrative (Details)	12 Months Ended
	Dec. 31, 2023 USD ($) loan	Dec. 31, 2022 USD ($) loan	Dec. 31, 2021 USD ($) loan	Jan. 01, 2022 USD ($)	Dec. 31, 2020 USD ($)
Financing Receivable, Allowance for Credit Loss [Line Items]
Loan syndications, amount	$ 100,000,000
Financing receivable, excluding accrued interest, after allowance for credit loss	13,799,367,000	$ 13,420,317,000
Debt, long-term and short-term, combined amount	48,216,000	740,828,000
Mortgage loans partially or wholly-owned by others and serviced by the Company	77,200,000	84,000,000
Proceeds from sales of commercial loans held for investment	189,296,000	0	$ 0
Loss on sales of commercial loans	2,738,000	0	0
Financing receivable, excluding accrued interest, allowance for credit loss, period increase (decrease)	6,800,000
Financing receivable, allowance for credit loss, excluding accrued interest	$ 148,993,000	$ 142,211,000	97,787,000		$ 113,031,000
Financing receivable, allowance for credit loss to outstanding, percent, period increase (decrease)	2
Financing receivable, allowance for credit loss to outstanding, percent	1.07%	1.05%
Financing receivable, excluding accrued interest, allowance for credit loss, writeoff, period increase	$ 10,300,000
Financing receivable, excluding accrued interest, allowance for credit loss, writeoff	15,092,000	$ 4,831,000	$ 9,002,000
Total loans	$ 13,973,428,000	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
Number of loans modified during the preceding 12 months that subsequently defaulted | loan		1	0
Amount of loans modified during the preceding 12 months that subsequently defaulted		$ 1,000,000
Amounts charged-off on TDRs		0	$ 0
Residential Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, collateral dependent loans	$ 800,000	600,000
Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, collateral dependent loans	30,700,000	16,200,000
Unrated | Minimum
Financing Receivable, Allowance for Credit Loss [Line Items]
Lines of credit, exposure	100,000
Commercial and industrial | Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Proceeds from sales of commercial loans held for investment	214,200,000
Loss on sales of commercial loans	2,700,000
Financing receivable, allowance for credit loss, excluding accrued interest	26,959,000	26,859,000	18,018,000		26,617,000
Financing receivable, excluding accrued interest, allowance for credit loss, writeoff	13,000	269,000	1,558,000
Total loans	3,034,068,000	3,150,946,000
Business banking | Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	14,913,000	16,189,000	10,983,000		13,152,000
Financing receivable, excluding accrued interest, allowance for credit loss, writeoff	4,645,000	2,292,000	5,091,000
Total loans	1,085,763,000	1,090,492,000
Business banking | Line of Credit | Unrated | Commercial Portfolio Segment | Maximum
Financing Receivable, Allowance for Credit Loss [Line Items]
Lines of credit, exposure	1,500,000
Unfunded Loan Commitment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	14,100,000	13,200,000		$ 11,100,000
Residential real estate | Residential Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Accrued interest purchase	32,000,000	380,200,000
Amortized cost balance of loans purchased	385,500,000	376,100,000
Financing receivable, allowance for credit loss, excluding accrued interest	25,954,000	28,129,000	6,556,000		6,435,000
Financing receivable, excluding accrued interest, allowance for credit loss, writeoff	0	0	35,000
Total loans	$ 2,565,485,000	$ 2,460,849,000
Number of loans in process of foreclosure | loan	2	0
Mortgage loans in process of foreclosure, amount	$ 200,000
Consumer home equity | Consumer Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	5,595,000	$ 6,454,000	3,722,000		$ 3,744,000
Financing receivable, excluding accrued interest, allowance for credit loss, writeoff	7,000	1,000	24,000
Total loans	$ 1,208,231,000	$ 1,187,547,000
Number of loans in process of foreclosure | loan	3	0
Mortgage loans in process of foreclosure, amount	$ 200,000
Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest		$ (1,143,000)	27,086,000
Cumulative effect accounting adjustment | Commercial and industrial | Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest		47,000	11,533,000
Cumulative effect accounting adjustment | Business banking | Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest		(140,000)	6,160,000
Cumulative effect accounting adjustment | Unfunded Loan Commitment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest				$ 1,000,000
Cumulative effect accounting adjustment | Residential real estate | Residential Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest		(849,000)	13,489,000
Cumulative effect accounting adjustment | Consumer home equity | Consumer Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest		(201,000)	$ 1,857,000
Short-term FHLB advances
Financing Receivable, Allowance for Credit Loss [Line Items]
FHLB advances	17,700,000	704,100,000
Federal Reserve Bank Advances
Financing Receivable, Allowance for Credit Loss [Line Items]
Debt, long-term and short-term, combined amount	0	0
Asset Pledged as Collateral | Short-term FHLB advances
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, excluding accrued interest, after allowance for credit loss	4,600,000,000	3,900,000,000
Asset Pledged as Collateral | Federal Reserve Bank Advances
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, excluding accrued interest, after allowance for credit loss	$ 1,100,000,000	$ 1,100,000,000