| **Investment Securities**                              | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
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| **Investments, Debt and Equity Securities [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
| Investment Securities                                  | Investment SecuritiesBelow is an analysis of the amortized cost and estimated fair values of securities available for sale at: June 30, 2014 December 31, 2013 AmortizedCost GrossUnrealizedGains GrossUnrealizedLosses EstimatedFair Value AmortizedCost GrossUnrealizedGains GrossUnrealizedLosses EstimatedFair Value (dollars in thousands)Obligations of U.S. Government Agencies:               Mortgage-Backed Securities – Residential$20,686 $2,617 $— $23,303 $22,639 $2,624 $(59) $25,204Obligations of U.S. Government-Sponsored Enterprises:             Mortgage-Backed Securities – Residential1,001,669 15,257 (13,807) 1,003,119 1,009,519 12,531 (27,163) 994,887Mortgage-Backed Securities – Commercial88 2 — 90 104 1 — 105Other Government-Sponsored Enterprises269,175 15 (803) 268,387 267,971 81 (1,927) 266,125Obligations of States and Political Subdivisions15,738 156 (5) 15,889 80 — — 80Corporate Securities6,688 561 — 7,249 6,693 328 — 7,021Pooled Trust Preferred Collateralized Debt Obligations41,851 109 (13,806) 28,154 42,040 — (18,517) 23,523Total Debt Securities1,355,895 18,717 (28,421) 1,346,191 1,349,046 15,565 (47,666) 1,316,945Equities1,420 — — 1,420 1,420 — — 1,420Total Securities Available for Sale$1,357,315 $18,717 $(28,421) $1,347,611 $1,350,466 $15,565 $(47,666) $1,318,365Mortgage backed securities include mortgage backed obligations of U.S. Government agencies and obligations of U.S. Government-sponsored enterprises. These obligations have contractual maturities ranging from less than one year to approximately 30 years with lower anticipated lives to maturity due to prepayments. All mortgage backed securities contain a certain amount of risk related to the uncertainty of prepayments of the underlying mortgages. Interest rate changes have a direct impact upon prepayment speeds, therefore First Commonwealth uses computer simulation models to test the average life and yield volatility of all mortgage backed securities under various interest rate scenarios to monitor the potential impact on earnings and interest rate risk positions.Expected maturities will differ from contractual maturities because issuers may have the right to call or repay obligations with or without call or prepayment penalties. Other fixed income securities within the portfolio also contain prepayment risk.The amortized cost and estimated fair value of debt securities available for sale at June 30, 2014, by contractual maturity, are shown below.  AmortizedCost EstimatedFair Value (dollars in thousands)Due within 1 year$2,600 $2,601Due after 1 but within 5 years266,575 265,786Due after 5 but within 10 years8,402 8,506Due after 10 years55,875 42,786 333,452 319,679Mortgage-Backed Securities (a)1,022,443 1,026,512Total Debt Securities$1,355,895 $1,346,191 (a)Mortgage Backed Securities include an amortized cost of $20.7 million and a fair value of $23.3 million for Obligations of U.S. Government agencies issued by Ginnie Mae and an amortized cost of $1,001.8 million and a fair value of $1,003.2 million for Obligations of U.S. Government-sponsored enterprises issued by Fannie Mae and Freddie Mac. Proceeds from sales, gross gains (losses) realized on sales, maturities and other-than-temporary impairment charges related to securities available for sale were as follows for the six months endedJune 30: 2014 2013 (dollars in thousands)Proceeds from sales$— $42Gross gains (losses) realized:   Sales Transactions:   Gross gains$— $4Gross losses— — — 4Maturities and impairment   Gross gains2 4Gross losses— — 2 4Net gains and impairment$2 $8Securities available for sale with an estimated fair value of $511.9 million and $594.9 million were pledged as of June 30, 2014 and December 31, 2013, respectively, to secure public deposits and for other purposes required or permitted by law. |

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| - Definition
The entire disclosure for  investments in certain debt and equity securities.
+ References
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