Document And Entity Information - shares	3 Months Ended
	Dec. 31, 2018	Jan. 31, 2019
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Entity Registrant Name	First Savings Financial Group Inc
Entity Central Index Key	0001435508
Current Fiscal Year End Date	--09-30
Entity Filer Category	Accelerated Filer
Trading Symbol	FSFG
Entity Common Stock, Shares Outstanding		2,304,310
Entity Emerging Growth Company	false
Entity Small Business	true