The aggregate principal amount of loan provided .

No definition available.

Name:	mara_FinancingReceivablesAmountOfLoanProvided
Namespace Prefix:	mara_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount commitments to lend additional funds on restructured loans.

+ References

No definition available.

+ Details

Name:	mara_FinancingReceivablesCommitmentsToLendAdditionalFundsOnRestructuredLoans
Namespace Prefix:	mara_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the maximum loan modification potential extension period provided by the Bank on a case by case basis to borrowers who were current in their payments at the inception of the loan modification program due to COVID-19.

+ References

No definition available.

+ Details

Name:	mara_FinancingReceivablesLoanModificationPotentialExtensionPeriodMaximum
Namespace Prefix:	mara_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of loans provided during period.

+ References

No definition available.

+ Details

Name:	mara_FinancingReceivablesNumberOfLoansProvided
Namespace Prefix:	mara_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the threshold loan modification period provided by the Bank due to COVID-19.

+ References

No definition available.

+ Details

Name:	mara_FinancingReceivablesThresholdLoanModificationPeriodDueToCovid19
Namespace Prefix:	mara_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=us-gaap_PaymentDeferralMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoansInsuredOrGuaranteedByGovernmentAuthoritiesAxis=mara_PaycheckProtectionLoansUnderCRESActMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans - Loan modification (Details)	3 Months Ended		12 Months Ended
Loans - Loan modification (Details)	Sep. 30, 2021 USD ($) loan	Sep. 30, 2020 USD ($)	Jun. 30, 2021 loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans modified	0	0
Commitments to lend additional funds on restructured loans	$ 0
Threshold loan modification period due to COVID19	3 months
Loan modification potential extension period, maximum, due to COVID 19	6 months
Payment Deferral
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans provided \| loan			56
Loans provided	$ 20,000,000.0
Paycheck Protection Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans provided \| loan	277
Loans provided	$ 18,500,000