Investments in Mortgage Revenue Bonds - Schedule of MRBs Eliminated (Details)	9 Months Ended
Sep. 30, 2019 USD ($) Unit
Schedule Of Available For Sale Securities [Line Items]
Units \| Unit	2,886
Mortgage Revenue Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Principal Outstanding at Date of Restructuring \| $	$ 13,960,000
Mortgage Revenue Bonds [Member] \| Avistar at Copperfield [Member] \| Series B [Member] \| Houston, TX [Member]
Schedule Of Available For Sale Securities [Line Items]
Month Restructured	May
Units \| Unit	192
Original Maturity Date	Jun. 01, 2054
Base Interest Rate	12.00%
Principal Outstanding at Date of Restructuring \| $	$ 4,000,000
Mortgage Revenue Bonds [Member] \| Avistar at Wilcrest [Member] \| Series B [Member] \| Houston, TX [Member]
Schedule Of Available For Sale Securities [Line Items]
Month Restructured	May
Units \| Unit	88
Original Maturity Date	Jun. 01, 2054
Base Interest Rate	12.00%
Principal Outstanding at Date of Restructuring \| $	$ 1,550,000
Mortgage Revenue Bonds [Member] \| Avistar at Wood Hollow [Member] \| Series B [Member] \| Austin,TX [Member]
Schedule Of Available For Sale Securities [Line Items]
Month Restructured	May
Units \| Unit	409
Original Maturity Date	Jun. 01, 2054
Base Interest Rate	12.00%
Principal Outstanding at Date of Restructuring \| $	$ 8,410,000

Investment owned, restructured month.

No definition available.

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Namespace Prefix:	atax_
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Balance Type:	na
Period Type:	duration

- Definition

Mortgage loans on real estate, restructuring, face amount.

+ References

No definition available.

+ Details

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Namespace Prefix:	atax_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Maturity date of mortgage loan within investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 12
-Paragraph Column C
-Subsection 29

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29(Column C))
-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

+ Details

Name:	srt_MortgageLoanOnRealEstateFinalMaturityDate
Namespace Prefix:	srt_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Interest rate of mortgage loan within investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 12
-Paragraph Column B
-Subsection 29

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29(Column B))
-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

+ Details

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Namespace Prefix:	srt_
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Balance Type:	na
Period Type:	duration

- Definition

The number of units in a real estate property owned as of the balance sheet date.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
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

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- Details

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- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

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Namespace Prefix:
Data Type:	na
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- Details

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Namespace Prefix:
Data Type:	na
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- Details

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- Details

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- Details

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