Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Jun. 30, 2017
Document And Entity Information [Abstract]
Entity Registrant Name	AMERICA FIRST Multifamily INVESTORS, L.P.
Entity Central Index Key	0001059142
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY
Amendment Flag	false
Trading Symbol	ATAX
Entity Common Stock, Units Outstanding	0
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float		$ 358,504,922