Cover Page - USD ($)	12 Months Ended
	Sep. 30, 2020	Nov. 30, 2020	Mar. 31, 2020
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Sep. 30, 2020
Document Transition Report	false
Entity File Number	001-35231
Entity Registrant Name	MITEK SYSTEMS, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	87-0418827
Entity Address, Address Line One	600 B Street, Suite 100
Entity Address, City or Town	San Diego,
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	92101
City Area Code	619
Local Phone Number	269-6800
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	MITK
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
ICFR Auditor Attestation Flag	false
Entity Public Float			$ 317,317,789
Entity Common Stock, Shares Outstanding		42,522,293
Documents Incorporated by Reference	Portions of the registrant’s definitive proxy statement for the 2021 Annual Meeting of Stockholders to be filed with the Securities and Exchange Commission pursuant to Regulation 14A are incorporated by reference into Part III of this Form 10-K to the extent stated herein.
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Central Index Key	0000807863
Current Fiscal Year End Date	--09-30