| **Impairment of Investment Securities (Tables)**                                                                     | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
||
| **Impairment of Investment Securities Disclosure [Abstract]**                                                        |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
| Schedule of Unrealized Losses and Estimated Fair Values                                                              | The following table presents the gross unrealized losses and estimated fair values at March 31, 2013 by investment category and time frame for which securities have been in a continuous unrealized loss position:  Less Than 12 Months  12 Months or More  Total EstimatedFair Value GrossUnrealizedLosses  EstimatedFair Value GrossUnrealizedLosses  EstimatedFair Value GrossUnrealizedLosses (dollars in thousands)Obligations of U.S. Government Agencies:           Mortgage-Backed Securities – Residential$— $—   $13 $—(a)  $13 $—Obligations of U.S. Government- Sponsored Enterprises:           Mortgage-Backed Securities – Residential$248,747 $(2,153) $20 $—(a) $248,767 $(2,153)Other Government-Sponsored Enterprises$59,464 $(113) $— $— $59,464 $(113)Corporate Securities4,797 (30) — — 4,797 (30)Pooled Trust Preferred Collateralized Debt Obligations$— $—   $24,454 $(26,566) $24,454 $(26,566)Total Securities Available for Sale$313,008 $(2,296) $24,487 $(26,566) $337,495 $(28,862) (a)Gross unrealized losses related to these types of securities are less than $1 thousand.The following table presents the gross unrealized losses and estimated fair values at December 31, 2012 by investment category and time frame for which securities have been in a continuous unrealized loss position: Less Than 12 Months  12 Months or More  Total EstimatedFair Value GrossUnrealizedLosses  EstimatedFair Value GrossUnrealizedLosses  EstimatedFair Value GrossUnrealizedLosses (dollars in thousands)Obligations of U.S. Government Agencies:           Mortgage-Backed Securities – Residential$— $— $13 $—(a)  $13 $—Obligations of U.S. Government- Sponsored Enterprises:           Mortgage-Backed Securities – Residential76,296 (392) 21 —(a) 76,317 (392)Other Government-Sponsored Enterprises59,303 (72) — —   59,303 (72)Pooled Trust Preferred Collateralized Debt Obligations— — 23,316 (28,496) 23,316 (28,496)Total Securities Available for Sale$135,599 $(464) $23,350 $(28,496) $158,949 $(28,960) (a)Gross unrealized losses related to these types of securities are less than $1 thousand. |
| Pooled Trust Preferred Collateralized Debt Obligations                                                               | The following table provides information related to our pooled trust preferred collateralized debt obligations as of March 31, 2013:DealClass BookValue Estimated FairValue UnrealizedGain(Loss) Moody’s/FitchRatings NumberofBanks DeferralsandDefaultsas a % ofCurrentCollateral ExcessSubordinationas a % ofCurrentPerformingCollateral(dollars in thousands)Pre TSL ISenior $2 $2 $— Aa3/A 9 33.33% NMPre TSL IVMezzanine 1,830 1,160 (670) Caa2/CCC 6 27.07 80.70Pre TSL VMezzanine 55 56 1 C/–   3 100.00 —Pre TSL VIIMezzanine 3,686 3,513 (173) Ca/C 16 45.70 —Pre TSL VIIIMezzanine 1,868 1,007 (861) C/C 31 54.03 —Pre TSL IXMezzanine 2,277 1,054 (1,223) Ca/C 45 27.04 10.57Pre TSL XMezzanine 1,343 1,157 (186) Ca/C 48 34.74 —Pre TSL XIIMezzanine 5,400 2,553 (2,847) Ca/C 70 32.55 —Pre TSL XIIIMezzanine 12,719 5,561 (7,158) Ca/C 63 31.20 15.98Pre TSL XIVMezzanine 13,304 5,230 (8,074) Ca/C 61 36.03 31.67MMCap ISenior 1,219 1,203 (16) Aa2/A 16 54.75 631.19MMCap IMezzanine 867 520 (347) Ca/C 16 54.75 —MM Comm IXMezzanine 6,507 1,496 (5,011) Ca/CC 28 43.38 —Total  $51,077 $24,512 $(26,565)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| Cumulative Roll Forward of Credit Losses Recognized in Earnings for Debt Securities held and not Intended to be Sold | The following provides a cumulative roll forward of credit losses recognized in earnings for debt securities held and not intended to be sold: For the Three-Months Ended March 31, 2013 2012 (dollars in thousands)Balance, beginning (a)$43,274 $44,736Credit losses on debt securities for which other-than-temporary impairment was not previously recognized— —Additional credit losses on debt securities for which other-than-temporary impairment was previously recognized— —Increases in cash flows expected to be collected, recognized over the remaining life of the security (b)(283) (235)Balance, ending$42,991 $44,501 (a)The beginning balance represents credit related losses included in other-than-temporary impairment charges recognized on debt securities in prior periods.(b)Represents the increase in cash flows recognized in interest income during the period.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |

| X                                                                                                                                                                              |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**fcf_ImpairmentOfInvestmentSecuritiesDisclosureAbstract**Namespace Prefix:**fcf_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Pooled trust preferred collateralized debt obligations.
+ References
No definition available.
+ Details**Name:**fcf_PooledTrustPreferredCollateralizedDebtObligationsTableTextBlock**Namespace Prefix:**fcf_**Data Type:**nonnum:textBlockItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Tabular disclosure of the amount of other than temporary impairment (OTTI) related to credit losses recognized in earnings including: (a) the beginning balance of the amount related to credit losses on debt securities held by the investor at the beginning of the period for which a portion of an OTTI was recognized in other comprehensive income; (b) additions for the amount related to the credit loss for which an OTTI was not previously recognized; (c) reductions for securities sold during the period (realized); (d) reductions for securities for which the amount previously recognized in other comprehensive income was recognized in earnings because the investor intends to sell the security or more likely than not will be required to sell the security before recovery of its amortized cost basis; (e) additional increases to the amount related to the credit loss for which an OTTI was previously recognized when the investor does not intend to sell the security and it is not more likely than not that the investor will be required to sell the security before recovery of its amortized cost basis; (f) reductions for increases in cash flows expected to be collected that are recognized over the remaining life of the security; and (g) the ending balance of the amount related to credit losses on debt securities held by the entity at the end of the period for which a portion of an OTTI was recognized in other comprehensive income.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27340-111563Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Staff Position (FSP) -Number FAS115-1/124-1 -Paragraph 18B -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.
+ Details**Name:**us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsTableTextBlock**Namespace Prefix:**us-gaap_**Data Type:**nonnum:textBlockItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
For all investments in an unrealized loss position, including those for which other-than-temporary impairments have not been recognized in earnings (including investments for which a portion of an other-than-temporary impairment has been recognized in other comprehensive income), a tabular disclosure of the aggregate related fair value of investments with unrealized losses and the aggregate amount of unrealized losses (that is, the amount by which amortized cost basis exceeds fair value).
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27290-111563
+ Details**Name:**us-gaap_ScheduleOfUnrealizedLossOnInvestmentsTableTextBlock**Namespace Prefix:**us-gaap_**Data Type:**nonnum:textBlockItemType**Balance Type:**na**Period Type:**duration |