Document and Entity Information	3 Months Ended
	Mar. 31, 2018 shares
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q1
Trading Symbol	CK0001448038
Entity Registrant Name	Redwood Mortgage Investors IX
Entity Central Index Key	0001448038
Current Fiscal Year End Date	--12-31
Entity Filer Category	Smaller Reporting Company
Entity Common Stock, Shares Outstanding	0