Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Feb. 24, 2022	Jun. 30, 2021
Document Information
Entity Registrant Name	MERCHANTS BANCORP
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
Document Transition Report	false
Entity File Number	001-38258
Amendment Flag	false
Entity Incorporation, State or Country Code	IN
Entity Tax Identification Number	20-5747400
Entity Address, Address Line One	410 Monon Blvd.
Entity Address, City or Town	Carmel
Entity Address, State or Province	IN
Entity Address, Postal Zip Code	46032
City Area Code	317
Local Phone Number	569-7420
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Public Float			$ 669.0
Entity Common Stock, Shares Outstanding		43,267,776
Auditor Name	BKD, LLP
Auditor Firm ID	686
Auditor Location	Indianapolis, Indiana
Entity Central Index Key	0001629019
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Common Stock.
Document Information
Title of 12(b) Security	Common Stock, without par value
Trading Symbol	MBIN
Security Exchange Name	NASDAQ
Series A Preferred Stock
Document Information
Title of 12(b) Security	Series A Preferred Stock, without par value
Trading Symbol	MBINP
Security Exchange Name	NASDAQ
Series B Preferred Stock
Document Information
Title of 12(b) Security	Depositary Shares, each representing a 1/40th interest in a share of Series B Preferred Stock, without par value
Trading Symbol	MBINO
Security Exchange Name	NASDAQ
Series C Preferred Stock
Document Information
Title of 12(b) Security	Depositary Shares, each representing a 1/40th interest in a share of Series C Preferred Stock, without par value
Trading Symbol	MBINN
Security Exchange Name	NASDAQ