Line of credit facility increase in borrowing capacity.

No definition available.

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

- Definition

Line of credit facility periodic payment percentage of principal.

+ References

No definition available.

+ Details

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

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

States whether the entity was in compliance with the debt covenants throughout the reporting period, and describes facts and circumstances of any compliance failure.

+ References

+ Details

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

- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

+ Details

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

- Definition

Latest date the outstanding debt instruments are required to be repaid, in CCYY-MM-DD format.

+ References

+ Details

Name:	us-gaap_DebtInstrumentMaturityDateRangeEnd1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Earliest date the outstanding debt instruments are required to be repaid, in CCYY-MM-DD format.

+ References

+ Details

Name:	us-gaap_DebtInstrumentMaturityDateRangeStart1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ 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(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: 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(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: 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(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_LineOfCreditFacilityLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=atax_FirstExtensionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=atax_SecondExtensionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=atax_ThirdExtensionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_StatementScenarioAxis=us-gaap_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Unsecured Lines of Credit - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2018	May 31, 2017	Apr. 30, 2017	Mar. 31, 2016	Feb. 29, 2016
Line Of Credit Facility [Line Items]
Lines of credit	$ 50,000,000	$ 40,000,000
Unsecured Lines of Credit [Member]
Line Of Credit Facility [Line Items]
Line of credit facility maximum borrowing capacity	60,000,000	47,500,000
Lines of credit	50,000,000	$ 40,000,000
Bankers Trust [Member] \| Unsecured Lines of Credit [Member]
Line Of Credit Facility [Line Items]
Line of credit facility maximum borrowing capacity	$ 50,000,000				$ 50,000,000
Line of credit facility, increase in borrowing capacity					10,000,000
Debt instrument, maturity date range start	Jun. 30, 2018
Debt instrument, maturity date range end	Sep. 30, 2018
Debt instrument, covenant compliance	The Partnership is in compliance with all covenants at December 31, 2017.
Debt instrument, maturity date	May 31, 2019	May 31, 2019
Bankers Trust [Member] \| Unsecured Lines of Credit [Member] \| First Extension [Member]
Line Of Credit Facility [Line Items]
Principal amount repayment on extension	5.00%
Bankers Trust [Member] \| Unsecured Lines of Credit [Member] \| Second Extension [Member]
Line Of Credit Facility [Line Items]
Principal amount repayment on extension	10.00%
Bankers Trust [Member] \| Unsecured Lines of Credit [Member] \| Third Extension [Member]
Line Of Credit Facility [Line Items]
Principal amount repayment on extension	20.00%
Bankers Trust [Member] \| Unsecured Lines of Credit [Member] \| London Interbank Offered Rate [Member]
Line Of Credit Facility [Line Items]
Debt instrument variable rate	3.00%
Bankers Trust Operating [Member] \| Unsecured Lines of Credit [Member]
Line Of Credit Facility [Line Items]
Line of credit facility maximum borrowing capacity				$ 10,000,000	$ 7,500,000	$ 7,500,000	$ 5,000,000
Debt instrument variable rate	3.25%
Lines of credit	$ 0
Bankers Trust Operating [Member] \| Unsecured Lines of Credit [Member] \| Scenario, Forecast [Member]
Line Of Credit Facility [Line Items]
Lines of credit			$ 0