Cover Page - shares	9 Months Ended
	Sep. 30, 2023	Nov. 06, 2023
Entity Information [Line Items]
Document Quarterly Report	true
Document Transition Report	false
Amendment Flag	false
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31
Entity Registrant Name	FIRST COMMONWEALTH FINANCIAL CORP /PA/
Entity Central Index Key	0000712537
Entity File Number	001-11138
Entity Filer Category	Large Accelerated Filer
Entity Interactive Data Current	Yes
Entity Tax Identification Number	25-1428528
Entity Address, Address Line One	601 Philadelphia Street
Entity Address, City or Town	Indiana
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	15701
City Area Code	724
Local Phone Number	349-7220
Entity Common Stock, Shares Outstanding		102,111,439
Entity Incorporation, State or Country Code	PA
Document Type	10-Q
Document Period End Date	Sep. 30, 2023
Title of 12(b) Security	Common Stock, $1.00 par value
Security Exchange Name	NYSE
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Trading Symbol	FCF
Entity Current Reporting Status	Yes