Investments - Summary of Fair Value of Investments Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Sep. 30, 2018
Assets
Total assets at fair value	$ 11,892	$ 8,448
Liabilities
Acquisition-related contingent consideration	1,180	3,051
Total liabilities at fair value	1,180	3,051
U.S. Treasury
Assets
Short-term investments	4,228	3,683
Corporate debt securities \| Financial
Assets
Short-term investments	686	2,847
Corporate debt securities \| Industrial
Assets
Short-term investments	1,368	1,918
Commercial paper \| Financial
Assets
Short-term investments	2,635
Commercial paper \| Industrial
Assets
Short-term investments	2,975
Quoted Prices in Active Markets (Level 1)
Assets
Total assets at fair value	4,228	3,683
Liabilities
Acquisition-related contingent consideration	0	0
Total liabilities at fair value	0	0
Quoted Prices in Active Markets (Level 1) \| U.S. Treasury
Assets
Short-term investments	4,228	3,683
Quoted Prices in Active Markets (Level 1) \| Corporate debt securities \| Financial
Assets
Short-term investments	0	0
Quoted Prices in Active Markets (Level 1) \| Corporate debt securities \| Industrial
Assets
Short-term investments	0	0
Quoted Prices in Active Markets (Level 1) \| Commercial paper \| Financial
Assets
Short-term investments	0
Quoted Prices in Active Markets (Level 1) \| Commercial paper \| Industrial
Assets
Short-term investments	0
Significant Other Observable Inputs (Level 2)
Assets
Total assets at fair value	7,664	4,765
Liabilities
Acquisition-related contingent consideration	0	0
Total liabilities at fair value	0	0
Significant Other Observable Inputs (Level 2) \| U.S. Treasury
Assets
Short-term investments	0	0
Significant Other Observable Inputs (Level 2) \| Corporate debt securities \| Financial
Assets
Short-term investments	686	2,847
Significant Other Observable Inputs (Level 2) \| Corporate debt securities \| Industrial
Assets
Short-term investments	1,368	1,918
Significant Other Observable Inputs (Level 2) \| Commercial paper \| Financial
Assets
Short-term investments	2,635
Significant Other Observable Inputs (Level 2) \| Commercial paper \| Industrial
Assets
Short-term investments	2,975
Significant Unobservable Inputs (Level 3)
Assets
Total assets at fair value	0	0
Liabilities
Acquisition-related contingent consideration	1,180	3,051
Total liabilities at fair value	1,180	3,051
Significant Unobservable Inputs (Level 3) \| U.S. Treasury
Assets
Short-term investments	0	0
Significant Unobservable Inputs (Level 3) \| Corporate debt securities \| Financial
Assets
Short-term investments	0	0
Significant Unobservable Inputs (Level 3) \| Corporate debt securities \| Industrial
Assets
Short-term investments	0	$ 0
Significant Unobservable Inputs (Level 3) \| Commercial paper \| Financial
Assets
Short-term investments	0
Significant Unobservable Inputs (Level 3) \| Commercial paper \| Industrial
Assets
Short-term investments	$ 0

No definition available.

Name:	us-gaap_AssetsAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26610-111562

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesDebtSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as current.

+ References

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of liability recognized arising from contingent consideration in a business combination.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 35
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=116859824&loc=d3e6819-128478

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 25
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6911189&loc=d3e6408-128476

+ Details

Name:	us-gaap_BusinessCombinationContingentConsiderationLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value of financial obligations, including, but not limited to, debt instruments, derivative liabilities, federal funds purchased and sold under agreements to repurchase, securities loaned or sold under agreements to repurchase, financial instruments sold not yet purchased, guarantees, line of credit, loans and notes payable, servicing liability, and trading liabilities.

+ References

No definition available.

+ Details

Name:	us-gaap_FinancialLiabilitiesFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_LiabilitiesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	invest_InvestmentAxis=mitk_FinancialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	invest_InvestmentAxis=mitk_IndustrialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CommercialPaperNotIncludedWithCashAndCashEquivalentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: