Retirement Plans, Pension and Postretirement Plans Table (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Fair Value Of Plan Assets As A Percentage Of Net Benefit Obligation	190.00%	171.00%
Change in Benefit Obligation
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment	$ 1,494	$ 0	$ 0
RAP
Change in Fair Value of Plan Assets
Fair value of plan assets at beginning of year	478,849	442,034
Actual return on plan assets	41,576	58,802
Employer contributions	0	0
Gross benefits paid	(22,629)	(21,987)
Fair value of plan assets at end of year(a)	497,796	478,849	442,034
Change in Benefit Obligation
Net benefit obligation at beginning of year	280,017	260,576
Service cost	7,779	8,244	7,263
Interest cost	6,570	8,185	9,752
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment	(1,494)	0
Actuarial (gain) loss	(8,921)	24,998
Gross benefits paid	(22,629)	(21,987)
Net benefit obligation at end of year(a)	261,321	280,017	260,576
Funded (unfunded) status	236,475	198,832
Noncurrent assets	236,475	198,832
Current liabilities	0	0
Noncurrent liabilities	0	0
Asset (liability) recognized on the consolidated balance sheets	$ 236,475	198,832
Defined Benefit Plan, Description	The Corporation has a noncontributory defined benefit RAP, covering substantially all employees who meet participation requirements. The benefits 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.
Postretirement Plan
Change in Fair Value of Plan Assets
Fair value of plan assets at beginning of year	$ 0	0
Actual return on plan assets	0	0
Employer contributions	201	210
Gross benefits paid	(201)	(210)
Fair value of plan assets at end of year(a)	0	0	0
Change in Benefit Obligation
Net benefit obligation at beginning of year	2,243	2,545
Service cost	0	0
Interest cost	52	78	104
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment	0	0
Actuarial (gain) loss	(119)	(169)
Gross benefits paid	(201)	(210)
Net benefit obligation at end of year(a)	1,975	2,243	$ 2,545
Funded (unfunded) status	(1,975)	(2,243)
Noncurrent assets	0	0
Current liabilities	(177)	(189)
Noncurrent liabilities	(1,798)	(2,055)
Asset (liability) recognized on the consolidated balance sheets	$ (1,975)	$ (2,243)
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.