INVESTMENTS IN DEBT SECURITIES (Bonds and Related Unrealized Gains and Losses) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Fair Value	$ 31,365	$ 97,190
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Unpaid principal balance of bond investments	30,885	92,332
Amortized Cost	20,797	59,565
Gross Unrealized Gains	10,568	37,625
Fair Value	$ 31,365	$ 97,190
FV as a % of UPB	102.00%	105.00%
Multifamily Tax-Exempt Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Unpaid principal balance of bond investments	$ 4,000	$ 65,162
Amortized Cost		38,653
Gross Unrealized Gains	6,026	33,564
Fair Value	$ 6,026	$ 72,217
FV as a % of UPB	151.00%	111.00%
Infrastructure Bond [Member]
Schedule of Available-for-sale Securities [Line Items]
Unpaid principal balance of bond investments	$ 26,885	$ 27,170
Amortized Cost	20,797	20,912
Gross Unrealized Gains	4,542	4,061
Fair Value	$ 25,339	$ 24,973
FV as a % of UPB	94.00%	92.00%

Available-For-Sale Securities, Debt Securities, Fair Value as a Percentage of Unpaid Principal Balance

No definition available.

Name:	mmac_AvailableForSaleSecuritiesDebtSecuritiesFairValueAsPercentageOfUnpaidPrincipalBalance
Namespace Prefix:	mmac_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The value of unpaid principal amount on investments securities.

+ References

No definition available.

+ Details

Name:	mmac_AvailableForSaleSecuritiesDebtSecuritiesUnPaidPrincipalBalance
Namespace Prefix:	mmac_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on 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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

+ Details

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

- Definition

Amortized cost 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 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

Reference 2: 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

+ Details

Name:	us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
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).

+ 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

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

- Details

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

- Details

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

- Details

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