Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Nov. 07, 2018
Entity Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Trading Symbol	FCF
Entity Registrant Name	FIRST COMMONWEALTH FINANCIAL CORP /PA/
Entity Central Index Key	0000712537
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		99,423,275
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Current Reporting Status	Yes