Document and Entity Information Document - shares	9 Months Ended
	Sep. 30, 2018	Nov. 06, 2018
Document Information [Line Items]
Entity Emerging Growth Company	false
Entity Small Business	false
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	FFBC
Entity Registrant Name	FIRST FINANCIAL BANCORP /OH/
Entity Central Index Key	0000708955
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		97,907,701