Document and Entity Information	9 Months Ended
	Sep. 30, 2018 shares
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
Entity Small Business	true
Entity Emerging Growth Company	false
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Amendment Flag	false
Trading Symbol	ATAX
Entity Common Stock, Units Outstanding	0