| **Commitments and Contingent Liabilities**              | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               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| **Commitments and Contingencies Disclosure [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  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| Commitments and Contingent Liabilities                  | Commitments and Contingent LiabilitiesCommitments and Letters of CreditStandby letters of credit and commercial letters of credit are conditional commitments issued by First Commonwealth to guarantee the performance of a customer to a third party. The contract or notional amount of these instruments reflects the maximum amount of future payments that First Commonwealth could be required to pay under the guarantees if there were a total default by the guaranteed parties, without consideration of possible recoveries under recourse provisions or from collateral held or pledged. In addition, many of these commitments are expected to expire without being drawn upon; therefore, the total commitment amounts do not necessarily represent future cash requirements.The following table identifies the notional amount of those instruments at: September 30, 2016 December 31, 2015 (dollars in thousands)Financial instruments whose contract amounts represent credit risk:   Commitments to extend credit$1,598,318 $1,643,187Financial standby letters of credit17,760 17,843Performance standby letters of credit28,110 26,497Commercial letters of credit1,528 1,672 The notional amounts outstanding as of September 30, 2016 include amounts issued in 2016 of $23 thousand in financial standby letters of credit, $2.9 million in performance standby letters of credit and $0.2 million commercial letters of credit.  A liability of $0.2 million has been recorded as of both September 30, 2016 and December 31, 2015 which represents the estimated fair value of letters of credit issued. The fair value of letters of credit is estimated based on the unrecognized portion of fees received at the time the commitment was issued.Unused commitments and letters of credit provide exposure to future credit loss in the event of nonperformance by the borrower or guaranteed parties. Management’s evaluation of the credit risk related to these commitments resulted in the recording of a liability of $4.0 million as of September 30, 2016 and $4.4 million as of December 31, 2015. This liability is reflected in "Other liabilities" in the Condensed Consolidated Statements of Financial Condition.  The credit risk evaluation incorporated probability of default, loss given default and estimated utilization for the next twelve months for each loan category and the letters of credit.Legal ProceedingsFirst Commonwealth and its subsidiaries are subject in the normal course of business to various pending and threatened legal proceedings in which claims for monetary damages are asserted. As of September 30, 2016, management, after consultation with legal counsel, does not anticipate that the aggregate ultimate liability arising out of litigation pending or threatened against First Commonwealth or its subsidiaries will be material to First Commonwealth’s consolidated financial position. On at least a quarterly basis, First Commonwealth assesses its liabilities and contingencies in connection with such legal proceedings. For those matters where it is probable that First Commonwealth will incur losses and the amounts of the losses can be reasonably estimated, First Commonwealth records an expense and corresponding liability in its consolidated financial statements. To the extent the pending or threatened litigation could result in exposure in excess of that liability, the amount of such excess is not currently estimable. Although not considered probable, the range of reasonably possible losses for such matters in the aggregate, beyond the existing recorded liability (if any), is between $0 and $7 million.  Although First Commonwealth does not believe that the outcome of pending litigation will be material to First Commonwealth’s consolidated financial position, it cannot rule out the possibility that such outcomes will be material to the consolidated results of operations and cash flows for a particular reporting period in the future.First Commonwealth Financial Corporation and First Commonwealth Bank were named defendants in an action commenced August 27, 2015 by eight named plaintiffs that is pending in the Court of Common Pleas of Jefferson County, Pennsylvania.  The plaintiffs allege that the Bank repossessed motor vehicles, sold the vehicles and sought to collect deficiency balances in a manner that did not comply with the notice requirements of the Pennsylvania Uniform Commercial Code (UCC), charged inappropriate costs and fees, including storage costs for dates that a repossessed vehicle was not in storage, and wrongly filed forms with the Department of Motor Vehicles asserting that the Bank had complied with applicable laws relating to the repossession of the vehicles. The plaintiffs seek to pursue the action as a class action on behalf of the named plaintiffs and other similarly situated plaintiffs who had their automobiles repossessed and seek to recover damages under the UCC and the Pennsylvania Fair Credit Extension Uniformity Act.  First Commonwealth and the Bank contest the plaintiffs’ allegations and intend to oppose class certification.  The Bank has also asserted counterclaims for breach of contract, set-off and recoupment against the plaintiffs, individually, and as representatives of the putative class.  The Bank and counsel for the plaintiffs reached an agreement-in-principle to settle the litigation during the second quarter of 2016.  The parties are negotiating the terms of a definitive settlement agreement which would be subject to court approval and other customary conditions.  The estimated cost of the settlement to the Bank was recorded as a liability in the second quarter of 2016.  As set forth in the preceding paragraph, all current litigation matters, including this action, are believed to be within the range of reasonably possible losses set forth in the preceding paragraph. |

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| - Definition
The entire disclosure for commitments, contingencies, and guarantees.
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