| **Intangible Assets (Tables)**                                     | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
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| **Goodwill and Intangible Assets Disclosure [Abstract]**           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
| Changes in Balance of Unamortized Intangible Assets (goodwill)     | For intangible assets related to business combinations, the following is a summary of the changes in the balance of unamortized intangible assets (goodwill) during the years ended December 31, 2012, 2011 and 2010: (dollars in thousands) For the Twelve Months EndedDecember 31,  2012 2011 2010Gross balance at beginning of year $3,905 $— $—Accumulated impairment balance beginning of year — — —Effect of Granite merger 300 3,905 —Impairment — — —Accumulated balance at end of year $4,205 $3,905 $—                                                                                                                                                                                                                                                                                                                                                                                                                                               |
| Changes in Original Carrying Amount of Amortized Intangible Assets | For intangible assets related to business combinations, the following is a summary of the changes in the original carrying amount of amortized intangible assets during the years ended December 31, 2012, 2011 and 2010:(dollars in thousands) For the Twelve Months EndedDecember 31,  2012 2011 2010Balance at the beginning of the period $13,102 $8,202 $8,202Effect of Granite merger — 4,900 —Impairment — — —Balance at the end of the period $13,102 $13,102 $8,202For intangible assets related to business combinations, the following is a summary of the gross carrying amount and accumulated amortization of amortized intangible assets and the carrying amount of unamortized intangible assets:(dollars in thousands) As of December 31,  2012 2011Core deposit premium related to whole bank acquisitions:    Carrying amount $13,102 $13,102Accumulated amortization 6,332 4,925Net core deposit premium $6,770 $8,177 |
| Estimated Amortization Expense for Intangible Assets               | The following table presents the estimated amortization expense for intangible assets for each of the five calendar years ending December 31, 2017 and the estimated amount amortizable thereafter. These estimates are subject to change in future periods to the extent management determines it is necessary to make adjustments to the carrying value or estimated useful lives of amortized intangible assets.(dollars in thousands)EstimatedAmortizationExpense2013$1,40720141,40720151,38620168342017612Thereafter1,123Total$6,769                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |

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| - Definition
Tabular disclosure of the amount of amortization expense expected to be recorded in succeeding fiscal years for finite-lived intangible assets.
+ References
No definition available.
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| - Definition
Tabular disclosure of assets, excluding financial assets and goodwill, lacking physical substance with a finite life, by either major class or business segment.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=7658586&loc=d3e16323-109275Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=7658586&loc=d3e16265-109275
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| - Definition
Tabular disclosure of goodwill by reportable segment and in total which includes a rollforward schedule.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 142 -Paragraph 45 -Subparagraph c -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.Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 142 -Paragraph 47 -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.Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=14024403&loc=d3e13854-109267Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=14024403&loc=d3e13816-109267Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 142 -Paragraph 45 -Subparagraph e -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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