Cover Page - shares	6 Months Ended
	Jun. 30, 2022	Aug. 03, 2022
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2022
Document Transition Report	false
Entity Registrant Name	FIRST MERCHANTS CORP
Entity Incorporation, State or Country Code	IN
Entity File Number	001-41342
Entity Tax Identification Number	35-1544218
Entity Address, Address Line One	200 East Jackson Street
Entity Address, City or Town	Muncie
Entity Address, State or Province	IN
Entity Address, Postal Zip Code	47305-2814
City Area Code	765
Local Phone Number	747-1500
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		59,490,370
Entity Central Index Key	0000712534
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q2
Amendment Flag	false
Common Stock, $0.125 stated value per share
Entity Information [Line Items]
Title of 12(b) Security	Common Stock, $0.125 stated value per share
Trading Symbol	FRME
Security Exchange Name	NASDAQ
Depositary Shares, each representing a 1/100th interest in a share of Non-Cumulative Perpetual Preferred Stock, Series A
Entity Information [Line Items]
Title of 12(b) Security	Depositary Shares, each representing a 1/100th interest in a share of Non-Cumulative Perpetual Preferred Stock, Series A
Trading Symbol	FRMEP
Security Exchange Name	NASDAQ