Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Mar. 06, 2020	Jun. 28, 2019
Document And Entity Information [Abstract]
Entity Registrant Name	First Internet Bancorp
Entity Central Index Key	0001562463
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		9,754,964
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Period Focus (Q1,Q2,Q3,FY)	FY
Document Fiscal Year Focus	2019
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Small Business	true
Entity Voluntary Filers	No
Entity Shell Company	false
Entity Emerging Growth Company	false
Entity Public Float			$ 204.6