Assets percentage.

No definition available.

Name:	atax_AssetsPercentage
Namespace Prefix:	atax_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of Available for Sale Securities

+ References

No definition available.

+ Details

Name:	atax_NumberOfAvailableForSaleSecurities
Namespace Prefix:	atax_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of collateralized securities.

+ References

No definition available.

+ Details

Name:	atax_NumberOfCollateralizedSecurities
Namespace Prefix:	atax_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of partnership securities sold and eliminated.

+ References

No definition available.

+ Details

Name:	atax_NumberOfPartnershipSecuritiesSoldAndEliminated
Namespace Prefix:	atax_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of rental units financed by mortgage revenue bonds.

+ References

No definition available.

+ Details

Name:	atax_NumberOfRentalUnitsFinancedByMortgageRevenueBonds
Namespace Prefix:	atax_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of rental units under MF properties segment.

+ References

No definition available.

+ Details

Name:	atax_NumberOfRentalUnitsUnderMFPropertiesSegment
Namespace Prefix:	atax_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of segments where Tax Exempted and Other Investments.

+ References

No definition available.

+ Details

Name:	atax_NumberOfSegmentsWhereTaxExemptedAndOtherInvestments
Namespace Prefix:	atax_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Required rating for tax exempted investments other than mortgage revenue bonds.

+ References

No definition available.

+ Details

Name:	atax_RequiredRatingForTaxExemptedInvestmentsOtherThanMortgageRevenueBonds
Namespace Prefix:	atax_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of real estate properties owned as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfRealEstateProperties
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfReportableSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
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_SegmentReportingInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=atax_TaxExemptAndOtherInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=atax_MortgageBackedSecuritiesInvestmentsSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=atax_MortgageRevenueBondInvestmentsSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=us-gaap_RealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Segments - Additional Information (Details)	12 Months Ended
Segments - Additional Information (Details)	Dec. 31, 2017 Property Unit Segment Security Rating	Jan. 31, 2016 Security
Segment Reporting Information [Line Items]
Number of Reportable Segments \| Segment	4
Number of segments where tax exempted and other investments Reported \| Segment	3
Minimum [Member]
Segment Reporting Information [Line Items]
Required rating for tax exempted investments other than mortgage revenue bonds \| Rating	1
Maximum [Member]
Segment Reporting Information [Line Items]
Required rating for tax exempted investments other than mortgage revenue bonds \| Rating	4
Tax-exempt and Other Investments [Member]
Segment Reporting Information [Line Items]
Assets percentage	25.00%
MBS Securities Investments [Member]
Segment Reporting Information [Line Items]
Number of partnership securities sold and eliminated.		3
Mortgage Revenue Bond Investments Segment [Member]
Segment Reporting Information [Line Items]
Number of Available for Sale Securities	87
Mortgage Revenue Bond Investments Segment [Member] \| Residential Properties [Member]
Segment Reporting Information [Line Items]
Number of rental units financed by mortgage revenue bonds \| Unit	10,666
Mortgage Revenue Bond Investments Segment [Member] \| Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Number of collateralized securities	1
Real Estate [Member]
Segment Reporting Information [Line Items]
Number of Real Estate Properties \| Property	3
Number of rental units under MF properties segment. \| Unit	1,013