Fair Value of Assets and Liabilities - Non Recurring Basis (Details) - Non Recurring	Dec. 31, 2020	Jun. 30, 2020 USD ($)
Impaired loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Alternative Investment, Valuation Technique [Extensible List]	mara:CollateralValuationMember	mara:CollateralValuationMember
Foreclosed assets
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Alternative Investment, Valuation Technique [Extensible List]	mara:CollateralValuationMember	mara:CollateralValuationMember
Level 3 | Impaired loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Alternative Investment		$ 1,536,554
Alternative Investment, Measurement Input [Extensible List]	us-gaap:MeasurementInputDiscountRateMember	us-gaap:MeasurementInputDiscountRateMember
Level 3 | Foreclosed assets
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Alternative Investment		$ 64,080
Alternative Investment, Measurement Input [Extensible List]	us-gaap:MeasurementInputDiscountRateMember	us-gaap:MeasurementInputDiscountRateMember
Level 3 | Minimum | Impaired loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Alternative Investment, Measurement Input	0
Level 3 | Minimum | Foreclosed assets
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Alternative Investment, Measurement Input	0
Level 3 | Maximum | Impaired loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Alternative Investment, Measurement Input	0.57
Level 3 | Maximum | Foreclosed assets
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Alternative Investment, Measurement Input	0.65