| **Income Taxes**                     | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                        |
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| **Income Tax Disclosure [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                  |
| Income Taxes                         | Income TaxesAt September 30, 2015 and December 31, 2014, First Commonwealth had no material unrecognized tax benefits or accrued interest and penalties. If applicable, First Commonwealth will record interest and penalties as a component of noninterest expense. Federal and state tax years 2012 through 2014 were open for examination as of September 30, 2015. |

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No definition available.
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| - Definition
The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.
+ References
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