| **Fair Values of Financial Instruments (Tables)**                                                                                                                   | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
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| **Fair Value Disclosures [Abstract]**                                                                                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
| Fair Value Measurements of Assets and Liabilities Recognized in the Balance Sheets Measured at Fair Value on Recurring Basis                                        | The following table presents the fair value measurements of assets and liabilities recognized in the accompanying balance sheets measured at fair value on a recurring basis and the level within the ASC 820-10 fair value hierarchy in which the fair value measurements fall at December 31, 2016 and 2015.    Fair Value Measurements Using:    Quoted Prices in ActiveMarkets for Identical Assets Significant Other Observable Inputs SignificantUnobservable InputsDecember 31, 2016 Fair Value (Level 1) (Level 2) (Level 3)Available for sale securities:        U.S. Government-sponsored agency securities $100   $100  State and municipal 363,658   358,524 $5,134U.S. Government-sponsored mortgage-backed securities 312,292   312,292  Corporate obligations 31     31Equity securities 20,781 $18,765 2,012 4Interest rate swap asset 6,295   6,295  Interest rate cap 15   15  Interest rate swap liability 8,477   8,477      Fair Value Measurements Using:    Quoted Prices in ActiveMarkets for Identical Assets Significant Other Observable Inputs SignificantUnobservable InputsDecember 31, 2015 Fair Value (Level 1) (Level 2) (Level 3)Available for sale securities:        U.S. Government-sponsored agency securities $104   $104  State and municipal 305,911   300,014 $5,897U.S. Government-sponsored mortgage-backed securities 346,266   346,266  Certificates of deposit 2,176  2,176  Corporate obligations 31     31Equity securities 3,912   3,908 4Interest rate swap asset 4,938   4,938  Interest rate cap 36   36  Interest rate swap liability 8,070   8,070   |
| Reconciliation of Beginning and Ending Balances of Recurring Fair Value Measurements Recognized in the Balance Sheets using Significant Unobservable Level 3 Inputs | The following is a reconciliation of the beginning and ending balances of recurring fair value measurements recognized in the accompanying balance sheets using significant unobservable Level 3 inputs for year ended December 31, 2016 and 2015. Available for Sale Securities For The Year Ended December 31, 2016 December 31, 2015Beginning Balance$5,932 $6,646Included in other comprehensive income(223) 199Principal payments(540) (913)Ending balance$5,169 $5,932                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
| Description of Valuation Methodologies Used for Instruments Measured at Fair Value on a Non-Recurring Basis and Recognized in the Balance Sheets                    | Following is a description of valuation methodologies used for instruments measured at fair value on a non-recurring basis and recognized in the accompanying balance sheets, as well as the general classification of such instruments pursuant to the valuation hierarchy for year ended December 31, 2016 and 2015.  Fair Value Measurements Using  Quoted Prices in ActiveMarkets for Identical AssetsSignificant Other Observable InputsSignificantUnobservable InputsDecember 31, 2016Fair Value(Level 1)(Level 2)(Level 3)Impaired Loans (collateral dependent)$15,318$15,318Other real estate owned $1,612$1,612  Fair Value Measurements Using  Quoted Prices in ActiveMarkets for Identical AssetsSignificant Other Observable InputsSignificantUnobservable InputsDecember 31, 2015Fair Value(Level 1)(Level 2)(Level 3)Impaired Loans (collateral dependent)$7,066  $7,066Other real estate owned$5,529  $5,529                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
| Unobservable Inputs Used in Recurring and Nonrecurring Level 3 Fair Value Measurements Other than Goodwill                                                          | The following table presents quantitative information about unobservable inputs used in recurring and nonrecurring Level 3 fair value measurements, other than goodwill, at December 31, 2016 and 2015.December 31, 2016Fair Value Valuation Technique Unobservable Inputs Range            (Weighted-Average)State and municipal securities$5,134 Discounted cash flow Maturity Call DateUS Muni BQ curveDiscount rate 1 month to 20 yearsA- to BBB-.69% - 5%        Corporate obligations and Equity securities$35 Discounted cash flow Risk free rateplus Premium for illiquidity 3 month LIBORplus 200 bps        Impaired loans (collateral dependent)$15,318 Collateral based measurements Discount to reflect current market conditions and ultimate collectability 0% - 10%                 (1%)        Other real estate owned$1,612 Appraisals Discount to reflect current market conditions 0% - 10%                 (9%)December 31, 2015Fair Value Valuation Technique Unobservable Inputs Range            (Weighted-Average)State and municipal securities$5,897 Discounted cash flow Maturity Call DateUS Muni BQ curveDiscount rate 1 month to 15 yearsA- to BBB-.80% - 5%        Corporate obligations and Equity securities$35 Discounted cash flow Risk free rateplus Premium for illiquidity 3 month LIBORplus 200 bps        Impaired loans (collateral dependent)$7,066 Collateral based measurements Discount to reflect current market conditions and ultimate collectability 0% - 50%                 (2%)        Other real estate owned$5,529 Appraisals Discount to reflect current market conditions 0% - 20%                 (2%)                                                                                                                                                                                                                                                                                                |
| Estimated Fair Values of Financial Instruments                                                                                                                      | The following table presents estimated fair values of the Corporation's financial instruments and the level within the fair value hierarchy in which the fair value measurements fall at December 31, 2016 and 2015. 2016 CarryingAmountQuoted Prices in Active Markets for Identical Assets (Level 1)Significant Other Observable Inputs(Level 2)Significant Unobservable Inputs(Level 3)Assets at December 31:   Cash and cash equivalents$127,927$127,927Interest-bearing time deposits24,45924,459Investment securities available for sale696,86218,765$672,928$5,169Investment securities held to maturity607,643597,24614,687Loans held for sale2,9292,929Loans5,073,6084,933,552Federal Home Loan Bank stock17,96417,964Interest rate swap asset6,3106,310Interest receivable26,19426,194Liabilities at December 31:Deposits$5,556,498$4,427,605$1,111,491Borrowings:Federal funds purchased120,349120,349Securities sold under repurchase agreements146,480146,449Federal Home Loan Bank advances298,923297,465Subordinated debentures and term loans128,445105,930Interest rate swap liability8,4778,477Interest payable3,1103,110 2015 CarryingAmountQuoted Prices in Active Markets for Identical Assets (Level 1)Significant Other Observable Inputs(Level 2)Significant Unobservable Inputs(Level 3)Assets at December 31:   Cash and cash equivalents$102,170$102,170Interest-bearing time deposits32,31532,315Investment securities available for sale658,400$652,468$5,932Investment securities held to maturity618,599598,08234,298Loans held for sale9,8949,894Loans4,631,3694,539,940Federal Reserve and Federal Home Loan Bank stock37,63337,633Interest rate swap asset4,9744,974Interest receivable24,41524,415Liabilities at December 31:Deposits$5,289,647$4,095,004$1,177,142Borrowings:Federal funds purchased49,72149,721Securities sold under repurchase agreements155,325155,325Federal Home Loan Bank advances235,652236,375Subordinated debentures and term loans127,846103,643Interest rate swap liability8,0708,070Interest payable3,0923,092                                                                                                                                                                                                                                                |

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| - Definition
Fair Value, Assets And Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation
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| - Definition
Tabular disclosure of the inputs and valuation techniques used to measure fair value, and a discussion of changes in valuation techniques and related inputs, if any, applied during the period to each separate class of assets, liabilities, and financial instruments classified in shareholders' equity that are measured on a recurring and/or nonrecurring basis.
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| - Definition
Tabular disclosure of assets and liabilities by class, including financial instruments measured at fair value that are classified in shareholders' equity, if any, that are measured at fair value on a nonrecurring basis in periods after initial recognition (for example, impaired assets). Disclosures may include, but are not limited to: (a) the fair value measurements recorded and the reasons for the measurements and (b) the level within the fair value hierarchy in which the fair value measurements are categorized in their entirety (levels 1, 2, 3).
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| - Definition
Tabular disclosure of the fair value of financial instruments, including financial assets and financial liabilities, and the measurements of those instruments, assets, and liabilities.
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| - Definition
Tabular disclosure of assets and liabilities, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, that are measured at fair value on a recurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3).
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