Mortgage Loan Servicing, Origination, and Loans Held for Sale (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Mortgage Loan Servicing, Origination, and Loans Held for Sale
Residential mortgages serviced for others	$ 6,700,000,000		$ 6,700,000,000		$ 6,600,000,000
Contractually specified servicing fees earned	4,300,000	$ 4,200,000	8,400,000	$ 8,300,000
Mortgage servicing rights	88,904,000		88,904,000		$ 85,164,000
Changes in the fair value of MSRs and its offsetting hedge.
Increase/(decrease) in fair value of MSRs	$ 830,000	$ 1,977,000	$ 3,214,000	$ 688,000
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	Revenue from Contract with Customer, Excluding Assessed Tax	Revenue from Contract with Customer, Excluding Assessed Tax
Decay of MSRs	$ (2,566,000)	$ (2,385,000)	$ (4,007,000)	$ (3,793,000)
(Loss) gain related to derivatives	(1,424,000)	(2,264,000)	(4,004,000)	(2,119,000)
Net effect on Consolidated Statements of Income	$ (3,160,000)	$ (2,672,000)	$ (4,797,000)	$ (5,224,000)
Characteristics and sensitivity analysis of the MSR
Composition of residential loans serviced for others	100.00%		100.00%		100.00%
Weighted average life (in years)			8 years 7 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)	$ (504,000)		$ (504,000)		$ (522,000)
Estimated impact on fair value of a 20% increase, Constant Prepayment rate (CPR)	(1,022,000)		(1,022,000)		(1,014,000)
Estimated impact on fair value of a 10% decrease, Constant Prepayment rate (CPR)	504,000		504,000		551,000
Estimated impact on fair value of a 20% decrease, Constant Prepayment rate (CPR)	1,018,000		$ 1,018,000		$ 1,128,000
Weighted average discount rate (as a percent)			10.90%		10.70%
Estimated impact on fair value of a 10% increase, Weighted average discount rate	(3,081,000)		$ (3,081,000)		$ (3,270,000)
Estimated impact on fair value of a 20% increase, Weighted average discount rate	(6,173,000)		(6,173,000)		(6,458,000)
Estimated impact on fair value of a 10% decrease, Weighted average discount rate	2,938,000		2,938,000		3,242,000
Estimated impact on fair value of a 20% decrease, Weighted average discount rate	5,550,000		5,550,000		6,283,000
Effect on fair value due to change in interest rates:
25 basis point increase	1,621,000		1,621,000		1,647,000
50 basis point increase	3,078,000		3,078,000		3,189,000
25 basis point decrease	(1,758,000)		(1,758,000)		(1,723,000)
50 basis point decrease	$ (3,623,000)		$ (3,623,000)		$ (3,501,000)
Fixed-rate mortgage loans
Characteristics and sensitivity analysis of the MSR
Composition of residential loans serviced for others	100.00%		100.00%		100.00%