Percentage Of Target Award Opportunities Maximum In Certain Cases

No definition available.

Name:	fcf_PercentageOfTargetAwardOpportunitiesMaximumInCertainCases
Namespace Prefix:	fcf_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Performance Based Stock Awards Vesting Period

+ References

No definition available.

+ Details

Name:	fcf_PerformanceBasedStockAwardsVestingPeriod
Namespace Prefix:	fcf_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Performance Shares Awards As Percentage Of Target

+ References

No definition available.

+ Details

Name:	fcf_PerformanceSharesAwardsAsPercentageOfTarget
Namespace Prefix:	fcf_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Share Based Compensation Arrangement By Share Based Payment Award Percentage Of Target Award Participants Earn

+ References

No definition available.

+ Details

Name:	fcf_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfTargetAwardParticipantsEarn
Namespace Prefix:	fcf_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(ii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of shares issued under share-based payment arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockUnitsRSUMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Incentive Compensation Plan - Unvested Target Award (Detail) - shares																							1 Months Ended	12 Months Ended
	Sep. 11, 2023	Aug. 16, 2023	Mar. 27, 2023	Jan. 23, 2023	Dec. 16, 2022	Dec. 06, 2022	Mar. 28, 2022	Feb. 17, 2022	Jan. 03, 2022	Dec. 13, 2021	Dec. 09, 2021	Nov. 22, 2021	Nov. 19, 2021	Sep. 27, 2021	Jun. 14, 2021	Feb. 18, 2021	Feb. 20, 2020	Feb. 21, 2019	Nov. 26, 2018	May 29, 2018	Mar. 26, 2018	Feb. 26, 2018	Mar. 26, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding, beginning of the year, Shares																								311,265	286,015	250,800
Granted, Shares																								106,750	108,000	134,515
Vested, Shares																								(90,810)	(75,500)	(88,389)
Forfeited, Shares																								(10,140)	(7,250)	(10,911)
Outstanding, end of the year, Shares																								317,065	311,265	286,015
Performance Based Stock Awards Vesting Period				3 years				3 years								3 years	3 years	3 years
Share Based Compensation Arrangement By Share Based Payment Award Percentage Of Target Award Participants Earn				40.00%				40.00%								40.00%	40.00%	40.00%
Performance Shares Awards As Percentage Of Target				100.00%				100.00%								100.00%	100.00%	100.00%
Percentage Of Target Award Opportunities Maximum In Certain Cases				200.00%				200.00%								200.00%	200.00%	200.00%
Vesting period of restricted stock				0 years				0 years								0 years	0 years	0 years
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding, beginning of the year, Shares																								434,352	391,100	434,180
Granted, Shares																								162,774	200,503	143,400
Vested, Shares																								(143,412)	(157,251)	(158,531)
Forfeited, Shares																								0	0	(27,949)
Outstanding, end of the year, Shares																								453,714	434,352	391,100
Shares issued (in shares)	8,000	1,000	25,000		1,000	1,500	50,000	57,000	1,000	2,000	1,000	1,565	24,000	6,000	15,000	84,950	95,300		2,000	3,000	2,000	77,500	26,200
Vesting period of restricted stock	1 year	1 year	1 year		1 year	1 year	1 year	1 year	1 year	1 year	1 year	1 year	1 year	1 year	3 years	1 year	1 year		1 year	1 year	1 year	1 year	1 year
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Shares issued (in shares)				159,000,000				121,200,000								143,400,000	125,800,000	121,900,000