DEBT (Outstanding Debt Balances) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Debt, Carrying Value	$ 201,816	$ 149,187
Debt Instrument, Interest Rate, Effective Percentage	4.80%	4.30%
Asset Related Debt [Member]
Debt Instrument [Line Items]
Debt, Carrying Value	$ 3,500	$ 44,255
Debt Instrument, Interest Rate, Effective Percentage	5.00%	3.90%
Notes Payable and Other Debt - Bond Related [Member]
Debt Instrument [Line Items]
Debt, Due within one year		$ 317
Debt, Due after one year		$ 38,938
Debt Instrument, Interest Rate, Effective Percentage, Current Portion		4.00%
Debt Instrument, Interest Rate, Effective Percentage, Noncurrent Portion		3.70%
Non-bond related debt
Debt Instrument [Line Items]
Debt, Due within one year	$ 650	$ 1,500
Debt, Due after one year	2,850	$ 3,500
Debt, Carrying Value	$ 3,500
Debt Instrument, Interest Rate, Effective Percentage, Current Portion	5.00%	5.00%
Debt Instrument, Interest Rate, Effective Percentage, Noncurrent Portion	5.00%	5.00%
Other Debt [Member]
Debt Instrument [Line Items]
Debt, Carrying Value	$ 198,316	$ 104,932
Debt Instrument, Interest Rate, Effective Percentage	4.80%	4.50%
Subordinated Loan [Member]
Debt Instrument [Line Items]
Debt, Due within one year	$ 2,212	$ 2,232
Debt, Due after one year	$ 93,276	$ 95,490
Debt Instrument, Interest Rate, Effective Percentage, Current Portion	3.20%	3.70%
Debt Instrument, Interest Rate, Effective Percentage, Noncurrent Portion	3.20%	3.70%
Net Premium and Debt Issuance Costs	$ 7,400	$ 7,900
Notes Payable and Other Debt - Other Related Debt
Debt Instrument [Line Items]
Debt, Due within one year	6,828	0
Debt, Due after one year	$ 1,500	$ 7,210
Debt Instrument, Interest Rate, Effective Percentage, Current Portion	14.70%	0.00%
Debt Instrument, Interest Rate, Effective Percentage, Noncurrent Portion	5.00%	14.70%
Unamortized debt issue costs	$ 100	$ 200
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt, Due after one year	94,500
Debt, Carrying Value	$ 94,500
Debt Instrument, Interest Rate, Effective Percentage, Noncurrent Portion	5.60%
Debt Instrument, Interest Rate, Effective Percentage	5.60%
Unamortized debt issue costs	$ 2,700

Debt Instrument, Interest Rate, Effective Percentage, Current Portion

No definition available.

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

- Definition

Debt Instrument, Interest Rate, Effective Percentage, Noncurrent Portion

+ References

No definition available.

+ Details

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

- Definition

Amount of net premiums and debt issuance costs as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	mmac_NetPremiumAndDebtIssuanceCosts
Namespace Prefix:	mmac_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6036836-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateEffectivePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
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_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19,20)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Details

Name:	us-gaap_LongtermDebtTypeAxis=mmac_AssetRelatedDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=mmac_NotesPayableAndOtherDebtBondRelatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=mmac_NotesPayableAndOtherDebtNonBondRelatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=mmac_OtherDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SubordinatedDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=mmac_NotesPayableAndOtherDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: