| Schedule of fair value of financial assets and liabilities measured on a recurring basis | 
        
    |   | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    | (Dollars in Thousands) | 
      | 
    Level 1  Inputs | 
      | 
    Level 2  Inputs | 
      | 
    Level 3 Inputs | 
      | 
    Total Fair  Value | 
      | 
 
    | September 30, 2012 | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    | ASSETS: | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    | Securities available for sale: | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    | U.S. Treasury | 
      | 
    $ | 
    108,718 | 
      | 
    $ | 
     | 
      | 
    $ | 
     | 
      | 
    $ | 
    108,718 | 
      | 
 
    | U.S. Government Agency | 
      | 
      | 
    33,291 | 
      | 
      | 
    8,511 | 
      | 
      | 
     | 
      | 
      | 
    41,802 | 
      | 
 
    | States and Political Subdivisions | 
      | 
      | 
     | 
      | 
      | 
    70,561 | 
      | 
      | 
     | 
      | 
      | 
    70,561 | 
      | 
 
    | Mortgage-Backed Securities | 
      | 
      | 
     | 
      | 
      | 
    56,252 | 
      | 
      | 
     | 
      | 
      | 
    56,252 | 
      | 
 
    | Other Securities | 
      | 
      | 
     | 
      | 
      | 
    10,833 | 
      | 
      | 
     | 
      | 
      | 
    10,833 | 
      | 
 
    | LIABILITIES: | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    | Fair Value Swap | 
      | 
      | 
     | 
      | 
      | 
     | 
      | 
      | 
     | 
      | 
      | 
     | 
      | 
 
    |   | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    | December 31, 2011 | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    | ASSETS: | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    | Securities available for sale: | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    | U.S. Treasury | 
      | 
    $ | 
    169,464 | 
      | 
    $ | 
     | 
      | 
    $ | 
     | 
      | 
    $ | 
    169,464 | 
      | 
 
    | U.S. Government Agency | 
      | 
      | 
    14,737 | 
      | 
      | 
     | 
      | 
      | 
     | 
      | 
      | 
    14,737 | 
      | 
 
    | States and Political Subdivisions | 
      | 
      | 
     | 
      | 
      | 
    59,094 | 
      | 
      | 
     | 
      | 
      | 
    59,094 | 
      | 
 
    | Mortgage-Backed Securities | 
      | 
      | 
     | 
      | 
      | 
    52,497 | 
      | 
      | 
     | 
      | 
      | 
    52,497 | 
      | 
 
    | Other Securities | 
      | 
      | 
     | 
      | 
      | 
    11,357 | 
      | 
      | 
     | 
      | 
      | 
    11,357 | 
      | 
 
    | LIABILITIES: | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    | Fair Value Swap | 
      | 
      | 
     | 
      | 
      | 
     | 
      | 
      | 
    572 | 
      | 
      | 
    572 | 
      | 
 
 
 | 
      
      
        | Schedule of tabular disclosure of estimated fair values of significant financial instruments | 
        
    |   | 
      | 
      | 
      | 
      | 
      | 
      | 
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      | 
      | 
      | 
      | 
      | 
      | 
 
    |   | 
      | 
    September 30, 2012 | 
      | 
 
    | (Dollars in Thousands) | 
      | 
    Carrying Value | 
      | 
    Level 1  Inputs | 
      | 
    Level 2  Inputs | 
      | 
    Level 3  Inputs | 
      | 
 
    | ASSETS: | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    | Cash | 
      | 
    $ | 
    53,076 | 
      | 
    $ | 
    53,076 | 
      | 
    $ | 
     | 
      | 
    $ | 
     | 
      | 
 
    | Short-Term Investments | 
      | 
      | 
    314,318 | 
      | 
      | 
    314,318 | 
      | 
      | 
     | 
      | 
      | 
     | 
      | 
 
    | Investment Securities | 
      | 
      | 
    288,166 | 
      | 
      | 
    142,009 | 
      | 
      | 
    146,157 | 
      | 
      | 
     | 
      | 
 
    | Loans Held for Sale | 
      | 
      | 
    16,527 | 
      | 
      | 
     | 
      | 
      | 
    16,527 | 
      | 
      | 
     | 
      | 
 
    | Loans, Net of Allowance for Loan Losses | 
      | 
      | 
    1,486,546 | 
      | 
      | 
     | 
      | 
      | 
     | 
      | 
      | 
    1,357,305 | 
      | 
 
    |   | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    | LIABILITIES: | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    | Deposits | 
      | 
    $ | 
    2,020,594 | 
      | 
    $ | 
     | 
      | 
    $ | 
    2,021,069 | 
      | 
    $ | 
     | 
      | 
 
    | Short-Term Borrowings | 
      | 
      | 
    42,388 | 
      | 
      | 
     | 
      | 
      | 
    41,678 | 
      | 
      | 
     | 
      | 
 
    | Subordinated Notes Payable | 
      | 
      | 
    62,887 | 
      | 
      | 
     | 
      | 
      | 
    62,912 | 
      | 
      | 
     | 
      | 
 
    | Long-Term Borrowings | 
      | 
      | 
    38,126 | 
      | 
      | 
     | 
      | 
      | 
    41,406 | 
      | 
      | 
     | 
      | 
 
 
    |   | 
      | 
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      | 
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      | 
 
    |   | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    |   | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    |   | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    |   | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    |   | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    |   | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    |   | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    |   | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    |   | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    |   | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    |   | 
      | 
    December 31, 2011 | 
      | 
 
    | (Dollars in Thousands) | 
      | 
      | 
    Carrying Value | 
      | 
      | 
    Level 1  Inputs | 
      | 
      | 
    Level 2  Inputs | 
      | 
      | 
    Level 3  Inputs | 
      | 
 
    | ASSETS: | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    | Cash | 
      | 
    $ | 
    54,953 | 
      | 
    $ | 
    54,953 | 
      | 
    $ | 
     | 
      | 
    $ | 
     | 
      | 
 
    | Short-Term Investments | 
      | 
      | 
    330,361 | 
      | 
      | 
    330,361 | 
      | 
      | 
     | 
      | 
      | 
     | 
      | 
 
    | Investment Securities | 
      | 
      | 
    307,149 | 
      | 
      | 
    184,201 | 
      | 
      | 
    122,948 | 
      | 
      | 
     | 
      | 
 
    | Loans Held for Sale | 
      | 
      | 
    21,225 | 
      | 
      | 
     | 
      | 
      | 
    21,225 | 
      | 
      | 
     | 
      | 
 
    | Loans, Net of Allowance for Loan Losses | 
      | 
      | 
    1,576,423 | 
      | 
      | 
     | 
      | 
      | 
     | 
      | 
      | 
    1,464,588 | 
      | 
 
    |   | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    | LIABILITIES: | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
 
    | Deposits | 
      | 
    $ | 
    2,172,519 | 
      | 
    $ | 
     | 
      | 
    $ | 
    2,173,331 | 
      | 
    $ | 
     | 
      | 
 
    | Short-Term Borrowings | 
      | 
      | 
    43,372 | 
      | 
      | 
     | 
      | 
      | 
    42,021 | 
      | 
      | 
     | 
      | 
 
    | Subordinated Notes Payable | 
      | 
      | 
    62,887 | 
      | 
      | 
     | 
      | 
      | 
    62,858 | 
      | 
      | 
     | 
      | 
 
    | Long-Term Borrowings | 
      | 
      | 
    44,606 | 
      | 
      | 
     | 
      | 
      | 
    47,770 | 
      | 
      | 
     | 
      | 
 
 
 |