|**Commitments and Contingent Liabilities (Tables)**                 | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                         
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|**Commitments and Contingencies Disclosure [Abstract]**             |                                                                                                                                                                                                                                                                                                                                                                                        
|Notional Amount of Outstanding Commitments                          | The following table identifies the notional amount of those instruments at:September 30, 2013December 31, 2012(dollars in thousands)Financial instruments whose contract amounts represent credit risk:Commitments to extend credit$1,568,438$1,506,618Financial standby letters of credit40,24547,185Performance standby letters of credit34,08469,240Commercial letters of credit—685
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|                                                                    | September 30, 2013                                                                                                                                                                                                                                                                                                                                                                     
|                                                                    | (dollars in thousands)                                                                                                                                                                                                                                                                                                                                                                 
|Financial instruments whose contract amounts represent credit risk: |                                                                                                                                                                                                                                                                                                                                                                                        
|Commitments to extend credit                                        | $                                                                                                                                                                                                                                                                                                                                                                                      
|Financial standby letters of credit                                 | 40,245                                                                                                                                                                                                                                                                                                                                                                                 
|Performance standby letters of credit                               | 34,084                                                                                                                                                                                                                                                                                                                                                                                 
|Commercial letters of credit                                        | —                                                                                                                                                                                                                                                                                                                                                                                      

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