Mortgage Loan Servicing, Origination, and Loans Held for Sale (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Mortgage Loan Servicing, Origination, and Loans Held for Sale
Residential mortgages serviced for others	$ 6,600,000		$ 6,600,000
Contractually specified servicing fees earned	4,200	$ 4,100
Mortgage servicing rights	87,970		$ 85,164
Changes in the fair value of MSRs and its offsetting hedge.
Increase/(decrease) in fair value of MSRs	$ 2,384	$ (1,290)
Servicing Asset, Fair Value, Change in Fair Value, Valuation Input, Statement of Income or Comprehensive Income [Extensible Enumeration]	Revenue from Contract with Customer, Excluding Assessed Tax	Revenue from Contract with Customer, Excluding Assessed Tax
Decay of MSRs	$ (1,442)	$ (1,409)
(Loss) gain related to derivatives	(2,580)	145
Net effect on Consolidated Statements of Income	$ (1,638)	$ (2,554)
Characteristics and sensitivity analysis of the MSR
Composition of residential loans serviced for others	100.00%		100.00%
Weighted average life (in years)	8 years 14 days		8 years 10 days
Constant Prepayment rate (CPR) (as a percent)	7.00%		7.00%
Estimated impact on fair value of a 10% increase, Constant Prepayment rate (CPR)	$ (528)		$ (522)
Estimated impact on fair value of a 20% increase, Constant Prepayment rate (CPR)	(1,037)		(1,014)
Estimated impact on fair value of a 10% decrease, Constant Prepayment rate (CPR)	546		551
Estimated impact on fair value of a 20% decrease, Constant Prepayment rate (CPR)	$ 1,106		$ 1,128
Weighted average discount rate (as a percent)	10.80%		10.70%
Estimated impact on fair value of a 10% increase, Weighted average discount rate	$ (3,192)		$ (3,270)
Estimated impact on fair value of a 20% increase, Weighted average discount rate	(6,377)		(6,458)
Estimated impact on fair value of a 10% decrease, Weighted average discount rate	3,061		3,242
Estimated impact on fair value of a 20% decrease, Weighted average discount rate	5,804		6,283
Effect on fair value due to change in interest rates:
25 basis point increase	1,595		1,647
50 basis point increase	3,044		3,189
25 basis point decrease	(1,729)		(1,723)
50 basis point decrease	$ (3,548)		$ (3,501)
Fixed-rate mortgage loans
Characteristics and sensitivity analysis of the MSR
Composition of residential loans serviced for others	100.00%		100.00%

Not applicable.

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Represents the value of residential mortgages serviced for others, which are acquired through merger transaction.

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Represents the percentage of residential mortgages serviced for others, which are acquired through merger transaction.

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The hypothetical financial impact of a 25 basis point decrease in interest rates on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

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The hypothetical financial impact of a 25 basis point increase in interest rates on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

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The hypothetical financial impact of a 50 basis point decrease in interest rates on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

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The hypothetical financial impact of a 10 percent adverse decrease of the discount rate on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

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The hypothetical financial impact of a 10 percent adverse decrease of prepayment speed on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

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The hypothetical financial impact of a 10 percent adverse increase of the discount rate on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

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The hypothetical financial impact of a 20 percent adverse decrease of the discount rate on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

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The hypothetical financial impact of a 20 percent adverse decrease of prepayment speed on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

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Amount of increase (decrease) in fair value from changes in the assumptions or model used to calculate the fair value of a contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

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All amounts that, per contract, are due to the servicer in exchange for servicing the financial asset and would no longer be received by a servicer if the beneficial owners of the serviced assets (or their trustees or agents) were to exercise their actual or potential authority under the contract to shift the servicing to another servicer. Depending on the servicing contract, those fees may include some or all of the difference between the interest rate collected on the asset being serviced and the rate to be paid to the beneficial owners of the asset.

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Aggregate amount of servicing assets that are subsequently measured at fair value and servicing assets that are subsequently measured using the amortization method.

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Indicates line item in statement of income or comprehensive income that includes increase (decrease) in fair value from change in input used to calculate fair value of contract to service financial asset under which benefit of servicing is expected to more than adequately compensate servicer.

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Amount of increase (decrease) in fair value from changes in the inputs used to calculate the fair value of contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

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Amount of increase (decrease) in fair value from changes classified as other for a contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

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The increase (decrease) in the fair value of servicing assets that are subsequently measured at fair value.

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Discount rate used to estimate the fair value of servicing assets and servicing liabilities.

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Estimated rate of prepayments of principal on servicing assets and servicing liabilities.

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Weighted average life of financial assets and financial liabilities, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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