Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2022	Feb. 24, 2023
Document and Entity Information [Abstract]
Document Transition Report	false
Document Annual Report	true
Title of 12(b) Security	COMMON STOCK, $1 PAR VALUE
Entity Tax Identification Number	25-1428528
Entity Address, Address Line One	601 PHILADELPHIA STREET
Entity Address, Postal Zip Code	15701
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2022
Entity File Number	001-11138
City Area Code	724
Local Phone Number	349-7220
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	FY
Entity Registrant Name	FIRST COMMONWEALTH FINANCIAL CORP /PA/
Entity Central Index Key	0000712537
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		103,069,202
Security Exchange Name	NYSE
Entity Shell Company	false
Entity Small Business	false
Entity Address, City or Town	INDIANA,
Entity Address, State or Province	PA
Entity Incorporation, State or Country Code	PA
ICFR Auditor Attestation Flag	true
Entity Public Float	$ 1,235,063,508
Trading Symbol	FCF