Retirement Plans, Pension and Postretirement Plans Table (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Change in Fair Value of Plan Assets
Defined Benefit Plan, Plan Assets, Contributions by Employer	$ 0
Change in Benefit Obligation
Fair Value Of Plan Assets As A Percentage Of Net Benefit Obligation	237.00%	224.00%
RAP
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Description	The Corporation has a noncontributory defined benefit RAP, covering substantially all employees who meet participation requirements. The benefit allocations are based primarily on years of service and the employee’s compensation paid. Employees of acquired entities generally participate in the RAP after consummation of the business combinations. Any retirement plans of acquired entities are typically merged into the RAP after completion of the mergers, and credit is usually given to employees for years of service at the acquired institution for vesting and eligibility purposes.
Change in Fair Value of Plan Assets
Defined Benefit Plan, Plan Assets, Amount, Beginning Balance	$ 478,970	$ 453,457
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss)	55,988	43,676
Defined Benefit Plan, Plan Assets, Contributions by Employer	0	0
Defined Benefit Plan, Plan Assets, Benefits Paid	17,379	18,163
Defined Benefit Plan, Plan Assets, Amount, Ending Balance	517,579	478,970	$ 453,457
Change in Benefit Obligation
Defined Benefit Plan, Benefit Obligation, Beginning Balance	213,365	211,353
Defined Benefit Plan, Service Cost	3,007	3,027	3,189
Defined Benefit Plan, Interest Cost	11,540	11,173	10,887
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	8,250	5,975
Defined Benefit Plan, Benefit Obligation, Benefits Paid	17,379	18,163
Defined Benefit Plan, Benefit Obligation, Ending Balance	218,783	213,365	211,353
Defined Benefit Plan, Funded (Unfunded) Status of Plan	298,796	265,605
Assets for Plan Benefits, Defined Benefit Plan	298,796	265,605
Liability, Defined Benefit Plan, Current	0	0
Liability, Defined Benefit Plan, Noncurrent	0	0
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position, Total	$ 298,796	265,605
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Description	The Corporation also provides legacy healthcare access to a limited group of retired employees from a previous acquisition in the Postretirement Plan. There are no other active retiree healthcare plans.
Change in Fair Value of Plan Assets
Defined Benefit Plan, Plan Assets, Amount, Beginning Balance	$ 0	0
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss)	0	0
Defined Benefit Plan, Plan Assets, Contributions by Employer	190	183
Defined Benefit Plan, Plan Assets, Benefits Paid	190	183
Defined Benefit Plan, Plan Assets, Amount, Ending Balance	0	0	0
Change in Benefit Obligation
Defined Benefit Plan, Benefit Obligation, Beginning Balance	2,043	1,425
Defined Benefit Plan, Service Cost	0	0
Defined Benefit Plan, Interest Cost	105	73	78
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	(248)	729
Defined Benefit Plan, Benefit Obligation, Benefits Paid	190	183
Defined Benefit Plan, Benefit Obligation, Ending Balance	1,710	2,043	$ 1,425
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(1,710)	(2,043)
Assets for Plan Benefits, Defined Benefit Plan	0	0
Liability, Defined Benefit Plan, Current	185	212
Liability, Defined Benefit Plan, Noncurrent	1,525	1,832
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position, Total	$ (1,710)	$ (2,043)