| **Condensed Financial Information of First Commonwealth Financial Corporation (parent company only)** | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
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| **Condensed Financial Information of Parent Company Only Disclosure [Abstract]**                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
| Condensed Financial Information of First Commonwealth Financial Corporation (parent company only)     | Condensed Financial Information of First Commonwealth Financial Corporation (parent company only)Statements of Financial ConditionDecember 31, 2014 2013 (dollars in thousands)Assets   Cash$10,402 $8,370Loans24 27Investment in subsidiaries712,610 696,438Investment in unconsolidated subsidiary trusts2,182 2,182Investment in jointly-owned company8,749 8,559Premises and equipment, net4,287 6,376Receivable from subsidiaries— 267Dividends receivable from subsidiaries— 1,319Other assets50,988 62,633Total assets$789,242 $786,171Liabilities and Shareholders’ Equity   Accrued expenses and other liabilities$930 $2,307Subordinated debentures payable72,167 72,167Shareholders’ equity716,145 711,697Total liabilities and shareholders’ equity$789,242 $786,171Statements of IncomeFor the years ended December 31, 2014 2013 2012 (dollars in thousands)Interest and dividends$1 $1 $1Dividends from subsidiaries49,207 65,140 64,342Interest expense(2,335) (3,128) (5,711)Other income1,251 2,653 12,581Operating expense(6,766) (8,820) (19,061)Income (loss) before taxes and equity in undistributed (loss) earnings of subsidiaries41,358 55,846 52,152Applicable income tax benefits2,968 3,384 4,364Income before equity in undistributed (loss) earnings of subsidiaries44,326 59,230 56,516Equity in undistributed earnings (loss) of subsidiaries127 (17,748) (14,562)Net income$44,453 $41,482 $41,954 For the years ended December 31,Statements of Cash Flow2014 2013 2012 (dollars in thousands)Operating Activities     Net income$44,453 $41,482 $41,954Adjustments to reconcile net income to net cash provided by operating activities:     Depreciation and amortization2,150 3,030 3,719Net gain (loss) on sales of assets— 17 (107)(Increase) decrease in prepaid income taxes(487) 3,044 (3,044)Undistributed equity in subsidiaries(127) 17,748 14,562Other net13,077 12,964 8,789Net cash provided by operating activities59,066 78,285 65,873Investing Activities     Net change in loans3 4 4Purchases of premises and equipment(47) (123) (3,005)Proceeds from sale of other assets13 1,132 4,309Net cash (used in) provided by investing activities(31) 1,013 1,308Financing Activities     Repayments of subordinated debenture— (34,702) —Discount on dividend reinvestment plan purchases(65) (112) (92)Dividends paid(26,174) (22,344) (18,759)Proceeds from reissuance of treasury stock192 176 1,028Purchase of treasury stock(30,956) (33,439) (36,242)Stock option tax benefit— — 1Net cash used in financing activities(57,003) (90,421) (54,064)Net increase (decrease) in cash2,032 (11,123) 13,117Cash at beginning of year8,370 19,493 6,376Cash at end of year$10,402 $8,370 $19,493Cash dividends declared per common share were $0.28 for 2014, $0.23 for 2013 and $0.18 for 2012.First Commonwealth Financial Corporation has an unsecured $15.0 million line of credit with another financial institution. As of  December 31, 2014, there are no amounts outstanding on this line.  We are currently not meeting a debt covenant related to Return on Average Assets; however, a waiver has been received from the lender for this covenant. |

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| - Definition
The entire disclosure for condensed financial information, including the financial position, cash flows, and the results of operations of the registrant (parent company) as of the same dates or for the same periods for which audited consolidated financial statements are being presented. Alternatively, the details of this disclosure can be reported by the specific parent company taxonomy elements, indicating the appropriate date and period contexts in an instance document.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 06 -Article 9Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=7656940&loc=d3e5283-111683Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 12Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph c -Article 5Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 05 -Paragraph c -Article 7
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