Commitments and other guarantees.

No definition available.

Name:	atax_CommitmentsAndOtherGuaranteesLineItems
Namespace Prefix:	atax_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Construction loan maximum available amount.

+ References

No definition available.

+ Details

Name:	atax_ConstructionLoanMaximumAvailableAmount
Namespace Prefix:	atax_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Initial lease term expiration period.

+ References

No definition available.

+ Details

Name:	atax_InitialLeaseTermExpirationPeriod
Namespace Prefix:	atax_
Data Type:	xbrli:gYearMonthItemType
Balance Type:	na
Period Type:	duration

- Definition

Lease agreement annual renewable increase percentage.

+ References

No definition available.

+ Details

Name:	atax_LeaseAgreementAnnualRenewableIncreasePercentage
Namespace Prefix:	atax_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Lease agreement extended term.

+ References

No definition available.

+ Details

Name:	atax_LeaseAgreementExtendedTerm
Namespace Prefix:	atax_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Lease transaction annual increment percentage in rent.

+ References

No definition available.

+ Details

Name:	atax_LeaseTransactionAnnualIncrementPercentageInRent
Namespace Prefix:	atax_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The estimated maximum percentage of possible loss from the contingency.

+ References

No definition available.

+ Details

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

- Definition

Property loan receivable, gross - Amount before allowance of loans held in portfolio. Includes principal only.

+ References

No definition available.

+ Details

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

- Definition

Purchase commitment remaining maximum amount committed.

+ References

No definition available.

+ Details

Name:	atax_PurchaseCommitmentRemainingMaximumAmountCommitted
Namespace Prefix:	atax_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Year Of Guarantee Agreement Term Ending .

+ References

No definition available.

+ Details

Name:	atax_YearOfGuaranteeAgreementTermEnding
Namespace Prefix:	atax_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying value as of the balance sheet date of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.15(a))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.15(5))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Definition

Maximum amount of loss due to credit risk that, based on the gross fair value of the financial instrument, the entity would incur if parties to the financial instruments that make up the concentration failed completely to perform according to the terms of the contracts and the collateral or other security, if any, for the amount due proved to be of no value to the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13537-108611

+ Details

Name:	us-gaap_ConcentrationRiskCreditRiskFinancialInstrumentMaximumExposure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents the carrying value of a short-term real estate loan to finance building costs. The funds are disbursed as needed or in accordance with a prearranged plan; generally, a portion of the funds is disbursed at inception and the remainder as construction progresses. The money is repaid on completion of the project, usually from the proceeds of a mortgage loan. The rate is normally higher than the prime rate, and there is usually an origination fee. The effective yield on these loans tends to be high, and the lender has a security interest in the real property. Note that there are separate concepts for the current and noncurrent portions of long-term construction loans.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(19))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Indicates, if estimable, (as a percentage) the approximate extent to which the proceeds from liquidation of any assets held either as collateral or by third parties would be expected to cover the maximum potential amount of future payments under the guarantee or each group of similar guarantees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=82913245&loc=d3e12069-110248

+ Details

Name:	us-gaap_GuaranteeObligationsLiquidationProceedsPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=82913245&loc=d3e12069-110248

+ Details

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

- Definition

Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

+ References

No definition available.

+ Details

Name:	us-gaap_LeaseAndRentalExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Date which lease or group of leases is set to expire, in CCYY-MM-DD format.

+ References

No definition available.

+ Details

Name:	us-gaap_LeaseExpirationDate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14435-108349

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 9
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14557-108349

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

This element represents the payments that the lessee is obligated to make or can be required to make in connection with a property under the terms of an agreement classified as an operating lease, excluding contingent rentals and a guarantee by the lessee of the lessor's debt and the lessee's obligation to pay (apart from the rental payments) executory costs such as insurance, maintenance, and taxes.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=77902758&loc=d3e41499-112717

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 10
-Section 25
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77910348&loc=d3e34039-112682

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 10
-Section 55
-Paragraph 40
-Subparagraph (Note 3)
-URI http://asc.fasb.org/extlink&oid=82846649&loc=d3e38371-112697

+ Details

Name:	us-gaap_OperatingLeasesRentExpenseMinimumRentals
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The yearly payments due under the lease entered into in connection with the transaction involving the sale of property to another party and the lease of the property back to the seller.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=84164451&loc=d3e36991-112694

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 40
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=77913982&loc=d3e50796-112755

+ Details

Name:	us-gaap_SaleLeasebackTransactionAnnualRentalPayments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=atax_GreensOfPineGlenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=atax_OhioPropertiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=atax_The5050StudentHousingUNLMember
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_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=atax_VantageAtBrooksAndVantageAtNewBraunfelsMember
Namespace Prefix:
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Period Type:

Commitments and Contingencies - Additional Information (Details)	1 Months Ended		3 Months Ended
	Mar. 31, 2018 USD ($) Unit	Mar. 31, 2017 USD ($)	Mar. 31, 2018 USD ($) Unit	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Commitments And Other Guarantees [Line Items]
Property loans receivable	$ 36,824,339		$ 36,824,339		$ 36,907,688
Construction loan maximum available amount	30,800,000	$ 25,600,000	30,800,000	$ 25,600,000
Outstanding construction loan amount	0	$ 16,600,000	0	16,600,000
Concentration risk, credit risk, financial instrument, maximum exposure			554,300,000
Greens of Pine Glen [Member]
Commitments And Other Guarantees [Line Items]
Guarantor obligations, maximum exposure, undiscounted	$ 2,600,000		$ 2,600,000
Percentage of loss contingency, range of possible loss, maximum	75.00%		75.00%
Year of guarantee agreement term ending			2027
Ohio Properties [Member]
Commitments And Other Guarantees [Line Items]
Property loans receivable	$ 2,390,446		$ 2,390,446		2,390,446
Percentage of loss contingency, range of possible loss, maximum	75.00%		75.00%
Year of guarantee agreement term ending			2026
Loss contingency, range of possible loss, maximum	$ 4,100,000		$ 4,100,000
The 50/50 Student Housing--UNL [Member]
Commitments And Other Guarantees [Line Items]
Initial lease term expiration period			2038-03
Lease agreement extend term			5 years
Annual lease payments			$ 100
Minimum monthly rentals under lease agreement			$ 127,000
Annual increment percentage in lease rent			2.00%
Lease expiration date			Jul. 31, 2034
Lease agreement annual renewable increase percentage			3.00%
Accounts payable related to agreement	$ 105,000		$ 105,000		$ 125,000
Expenses related to the agreement			42,000	$ 42,000
Maximum [Member]
Commitments And Other Guarantees [Line Items]
Construction loan guarantee percentage on debt service coverage levels	50.00%	50.00%
Minimum [Member]
Commitments And Other Guarantees [Line Items]
Construction loan guarantee percentage on debt service coverage levels	25.00%	25.00%
Vantage at Brooks and Vantage at New Braunfels [Member]
Commitments And Other Guarantees [Line Items]
Property loans receivable	$ 17,000,000		$ 17,000,000
Number of units in real estate property \| Unit	2		2
Remaining maximum amount committed	$ 1,200,000		$ 1,200,000