Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2015	Nov. 03, 2015
Document Information [Line Items]
Entity Registrant Name	FIRST FINANCIAL CORP /IN/
Entity Central Index Key	0000714562
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding		12,703,869
Trading Symbol	THFF