| **Income Tax (Tables)**                                   | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
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| **Income Tax Disclosure [Abstract]**                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
| Reconciliation of Federal Statutory to Actual Tax Expense | The reconciliation between income tax expense expected at the U.S. federal statutory tax rate and the reported income tax expense is summarized in the following table for years ended December 31, 2016, 2015, 2014:201620152014Reconciliation of Federal Statutory to Actual Tax Expense:   Federal Statutory Income Tax at 35%$38,031$31,867$28,800Tax-exempt Interest Income(8,749)(7,083)(5,148)Basis Difference on Sale of Insurance Subsidiary2,252Stock Compensation273436Earnings on Life Insurance(1,486)(1,012)(1,271)Tax Credits(564)(583)(911)Other350190617Income Tax Expense$27,609$25,665$22,123                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
| Components of Income Tax Expense (Benefit)                | Income tax expense consists of the following components for the years ended December 31, 2016, 2015, 2014: 201620152014Income Tax Expense for the Year Ended December 31:  Currently Payable:  Federal$18,998$21,221$7,075StateDeferred:Federal8,2333,95214,538State378492510Income Tax Expense$27,609$25,665$22,123                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
| Deferred Tax Assets and Liabilities                       | Significant components of the net deferred tax assets (liabilities) resulting from temporary differences were as follows at December 31, 2016 and 2015: 20162015Deferred Tax Asset at December 31:  Assets:  Differences in Accounting for Loan Losses$26,315$25,867Differences in Accounting for Loan Fees1,918762Differences in Accounting for Loans and Securities5,6899,359Deferred Compensation3,4715,100Difference in Accounting for Pensions and Other Employee Benefits832,247Federal & State Income Tax Loss Carryforward and Credits16,64323,737Other4,2109,310Total Assets58,32976,382Liabilities:  Differences in Depreciation Methods8,2167,742State Income Tax237591Net Unrealized Gain on Securities Available for Sale5576,636Gain on FDIC Modified Whole Bank Transaction1,1261,405Other623717Total Liabilities10,75917,091Net Deferred Tax Asset Before Valuation Allowance47,57059,291Valuation allowance: Beginning Balance(15,736)(17,568)Decrease/(Increase) During the Year5,9211,832Ending Balance(9,815)(15,736)Net Deferred Tax Asset$37,755$43,555 |

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| - Definition
Tabular disclosure of the components of income tax expense attributable to continuing operations for each year presented including, but not limited to: current tax expense (benefit), deferred tax expense (benefit), investment tax credits, government grants, the benefits of operating loss carryforwards, tax expense that results from allocating certain tax benefits either directly to contributed capital or to reduce goodwill or other noncurrent intangible assets of an acquired entity, adjustments of a deferred tax liability or asset for enacted changes in tax laws or rates or a change in the tax status of the entity, and adjustments of the beginning-of-the-year balances of a valuation allowance because of a change in circumstances that causes a change in judgment about the realizability of the related deferred tax asset in future years.
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Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32639-109319
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| - Definition
Tabular disclosure of the components of net deferred tax asset or liability recognized in an entity's statement of financial position, including the following: the total of all deferred tax liabilities, the total of all deferred tax assets, the total valuation allowance recognized for deferred tax assets.
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Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32537-109319
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| - Definition
Tabular disclosure of the reconciliation using percentage or dollar amounts of the reported amount of income tax expense attributable to continuing operations for the year to the amount of income tax expense that would result from applying domestic federal statutory tax rates to pretax income from continuing operations.
+ References
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