Document and Entity Information	9 Months Ended
	Sep. 30, 2021 shares
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
No Trading Symbol Flag	true
Entity Registrant Name	REDWOOD MORTGAGE INVESTORS VIII
Entity Central Index Key	0000889123
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding	0
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
Document Quarterly Report	true
Document Transition Report	false
Entity File Number	000-27816
Entity Incorporation, State or Country Code	CA
Entity Tax Identification Number	94-3158788
Entity Address, Address Line One	177 Bovet Road
Entity Address, Address Line Two	Suite 520
Entity Address, City or Town	San Mateo
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94402
City Area Code	650
Local Phone Number	365-5341