| **Investment Securities (Tables)**                                                                                                              | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
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| **Investments, Debt and Equity Securities [Abstract]**                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
| Amortized Cost and Approximate Fair Values of Securities                                                                                        | The amortized cost, gross unrealized gains, gross unrealized losses and approximate market value of the investment securities at the dates indicated were: Amortized CostGross Unrealized GainsGross Unrealized LossesFair ValueAvailable for sale at December 31, 2012       U.S. Government-sponsored agency securities$4,475$165$4,640State and municipal148,18710,025$18158,194U.S. Government-sponsored mortgage-backed securities337,63110,99446348,579Corporate obligations6,1055,881224Equity securities1,7061,706Total available for sale498,10421,1845,945513,343Held to maturity at December 31, 2012 State and municipal117,2275,4891122,715U.S. Government-sponsored mortgage-backed securities243,79311,68115255,459Total held to maturity361,02017,17016378,174Total Investment Securities$859,124$38,354$5,961$891,517        Available for sale at December 31, 2011       U.S. Government-sponsored agency securities$99 $18   $117State and municipal136,857 10,496   147,353U.S. Government-sponsored mortgage-backed securities358,928 10,086 $16 368,998Corporate obligations5,765   5,572 193Equity securities1,830     1,830Total available for sale503,479 20,600 5,588 518,491Held to maturity at December 31, 2011       State and municipal120,171 3,785   123,956U.S. Government-sponsored mortgage-backed securities307,738 10,775   318,513Total held to maturity427,909 14,560   442,469Total Investment Securities$931,388 $35,160 $5,588 $960,960 |
| Debt Securities Credit Loss Recognized in Income, and Other Losses Recorded in Other Comprehensive Income                                       | The following table provides information about debt securities for which only a credit loss was recognized in income and other losses are recorded in other comprehensive income. Accumulated Credit Losses in  Accumulated Credit Losses in  2012 2011Credit losses on debt securities held:   Balance, January 1$11,355 $10,955Additions related to other-than-temporary losses not previously recognized 400Balance, December 31$11,355 $11,355                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
| Investments' Gross Unrealized Losses and Fair Value Aggregated by Investment Category and Length of Time in Continuous Unrealized Loss Position | The following table shows the Corporation’s gross unrealized losses and fair value, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position at December 31, 2012 and 2011:  Fair ValueGross Unrealized LossesFair ValueGross Unrealized LossesFair ValueGross Unrealized Losses Less than 12 Months12 Months or LongerTotalTemporarily Impaired Investment      Securities at December 31, 2012      State and municipal$4,524$19$4,524$19U.S. Government-sponsored mortgage-backed securities12,3206112,32061Corporate obligations$194$5,8811945,881Total Temporarily Impaired Investment Securities$16,844$80$194$5,881$17,038$5,961            Temporarily Impaired Investment      Securities at December 31, 2011      U.S. Government-sponsored mortgage-backed securities$6,176$16$6,176$16Corporate obligations$163$5,5721635,572Total Temporarily Impaired Investment Securities$6,176$16$163$5,572$6,339$5,588                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
| Amortized Cost and Fair Value of Available for Sale Securities and Held to Maturity Securities by Contractual Maturity                          | Expected maturities will differ from contractual maturities because issuers may have the right to call or prepay obligations with or without call or prepayment penalties. Available for SaleHeld to Maturity Amortized CostFair ValueAmortized CostFair ValueMaturity Distribution at December 31, 2012    Due in one year or less$4,366$4,415$2,590$2,594Due after one through five years14,76415,4682,5542,575Due after five through ten years54,14857,44257,81160,163Due after ten years85,48985,73354,27257,383 $158,767$163,058$117,227$122,715U.S. Government-sponsored mortgage-backed securities337,631348,579243,793255,459Equity securities1,7061,706Total Investment Securities$498,104$513,343$361,020$378,174                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |

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| - Definition
Tabular disclosure of fair value of investments in debt and equity securities in an unrealized loss position categorized neither as held-to-maturity nor trading securities.
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No definition available.
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Tabular disclosure of maturities of an entity's investments as well as any other information pertinent to the investments.
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| - Definition
Tabular disclosure of the amount of other than temporary impairment (OTTI) related to credit losses recognized in earnings including: (a) the beginning balance of the amount related to credit losses on debt securities held by the investor at the beginning of the period for which a portion of an OTTI was recognized in other comprehensive income; (b) additions for the amount related to the credit loss for which an OTTI was not previously recognized; (c) reductions for securities sold during the period (realized); (d) reductions for securities for which the amount previously recognized in other comprehensive income was recognized in earnings because the investor intends to sell the security or more likely than not will be required to sell the security before recovery of its amortized cost basis; (e) additional increases to the amount related to the credit loss for which an OTTI was previously recognized when the investor does not intend to sell the security and it is not more likely than not that the investor will be required to sell the security before recovery of its amortized cost basis; (f) reductions for increases in cash flows expected to be collected that are recognized over the remaining life of the security; and (g) the ending balance of the amount related to credit losses on debt securities held by the entity at the end of the period for which a portion of an OTTI was recognized in other comprehensive income.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27340-111563Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Staff Position (FSP) -Number FAS115-1/124-1 -Paragraph 18B -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.
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| - Definition
Tabular disclosure of unrealized gains and losses on investments.
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No definition available.
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