Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2021	May 05, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Entity Registrant Name	Civista Bancshares, Inc.
Entity Central Index Key	0000944745
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		15,622,721
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	001-36192
Entity Tax Identification Number	34-1558688
Entity Incorporation, State or Country Code	OH
Entity Address, Address Line One	100 East Water Street
Entity Address, City or Town	Sandusky
Entity Address, State or Province	OH
Entity Address, Postal Zip Code	44870
City Area Code	419
Local Phone Number	625-4121
Document Quarterly Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common
Trading Symbol	CIVB
Security Exchange Name	NASDAQ