Document And Entity Information - shares	3 Months Ended
	Mar. 31, 2020	May 01, 2020
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
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Document Type	10-Q
Document Period End Date	Mar. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		13,714,524