Derivatives - Schedule of Changes in Fair Value of Derivative Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Derivative [Line Items]
Increase (decrease) in other income	$ 375	$ (5,108)	$ 1,126	$ (5,643)

Change in the fair value of derivative assets and derivative liabilities attributable to credit risk included in other income.

No definition available.

Name:	fcf_ChangeInOtherIncomeDueToCreditRiskOnInterestRateSwaps
Namespace Prefix:	fcf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration