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Retirement Plans - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Employer contribution	3.00%
Employee contribution	80.00%
Contribution of employee matched with employer's contribution	4.00%
Contribution matched to employer's contribution	50.00%
Plan expense	$ 2,600,000	$ 2,500,000	$ 2,600,000
Commonwealth compensation to plan				4.00%
Commonwealth compensation to plan, additional				3.00%
Retirement Plan expense	$ 0	$ 86,000	$ 96,000
Minimum [Member]
Eligibility of participants	1.00%
Maximum [Member]
Eligibility of participants	25.00%

X

- Definition

Deferred Compensation Plan Net Of Contribution Expenses

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No definition available.

+ Details

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Balance Type:	debit
Period Type:	duration

X

- Definition

Defined Contribution Plan Employer Matching Contribution Percent For First Compensation Slab

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No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

X

- Definition

Defined Contribution Plan Employer Matching Contribution Percent For Next Compensation Slab

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No definition available.

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Participant Contribution On Pre Tax Basis Under Retirement Plan

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No definition available.

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Percentage Of Employees Eligible Compensation That Represents Maximum Amount Of Employer Matching Contributions To Four Zero One K Plan

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No definition available.

+ Details

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Balance Type:	na
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X

- Definition

Percentage Of Employers Contribution Based On Participants Compensation

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No definition available.

+ Details

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Namespace Prefix:	fcf_
Data Type:	num:percentItemType
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X

- Definition

Retirement Plan Expense

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No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

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No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

X

- Definition

Maximum percentage of employee gross pay, by the terms of the plan, that the employer may contribute to a defined contribution plan.

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No definition available.

+ Details

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