Manager and Other Related Parties - Additional Information (Details)		3 Months Ended		12 Months Ended
		Mar. 31, 2022 USD ($) MortgageLoan	Mar. 31, 2021 USD ($) MortgageLoan	Dec. 31, 2021 USD ($) MortgageLoan
Managers And Other Related Parties Details [Line Items]
Managers Share of net income or loss		1.00%
Liquidation offering proceeds, percentage		(7.00%)
Formation loan advances to RMC		$ 5,627,000
Remaining performance obligation, amount		3,265,000
Future redemptions of member's capital		1,800,000
Early withdrawal penalties	[1]	$ 0	$ 4,000
Reimbursement as a percentage of member's original purchase price		0.45%
Percentage of original purchase price, quarterly installment percentage		0.1125%
Payable to related parties		$ 3,000		$ 101,000
Receivables from manager				67,000
Payable due to the manager		55,000
Principal		$ 64,293,000		$ 81,097,000
Number of secured loans with prepaid interest | MortgageLoan		44		54
Five Performing Loan [Member]
Managers And Other Related Parties Details [Line Items]
Principal			$ 4,672,000
Mortgage Loans transferred On Real Estate Number Of Loans | MortgageLoan			5
Two Performing Loan [Member]
Managers And Other Related Parties Details [Line Items]
Principal			$ 868,000
Mortgage Loans transferred On Real Estate Number Of Loans | MortgageLoan			2
Accounts Payable And Cost Reimbursements [Member]
Managers And Other Related Parties Details [Line Items]
Receivable from related party		$ 68,000
Payable to related parties				$ 168,000
Redwood Mortgage Investors VIII [Member]
Managers And Other Related Parties Details [Line Items]
Total cost		$ 86,000	$ 65,000
RMC [Member]
Managers And Other Related Parties Details [Line Items]
Management Fee, Percentage		0.75%
Working Capital Reserve, Percentage		2.00%
Qualifying costs incurred		$ 187,000	146,000
Reimbursement of costs		$ 101,000	81,000
Administrative Fees, Percentage		1.00%
Administrative Fees Chargeable		$ 10,000	62,000
Loan Brokerage Commission Percent Minimum		1.50%
Loan Brokerage Commission Percent Maximum		5.00%
Loan Brokerage Commissions, Maximum Percent of Assets		4.00%
Loan Brokerage Commission		$ 13,000	161,000
Repayment of formation loan in annual installments		208,000
Future redemptions of member's capital		1,927,000	927,000
Early withdrawal penalties		3,000	$ 8,000
RMC [Member] | Accounts Payable And Cost Reimbursements [Member]
Managers And Other Related Parties Details [Line Items]
Receivable from related party		13,000
Payable to related parties		$ 3,000		$ 101,000
Maximum [Member]
Managers And Other Related Parties Details [Line Items]
Annual mortgage servicing fees, percentage		0.25%
Percentage of reimbursement of organization and offering expenses		4.50%
Reimbursement threshold		For each of forty (40) calendar quarters or portion thereof after December 31, 2015

[1] Beginning in 2022, RMC discontinued the specific allocation of early withdrawal penalties it received to the formation loan and to the amount owed for unallocated O&O expenses on redeeming-members’ accounts. Prior to 2022, the O&O expenses component of early withdrawal penalties were applied as a reduction to O&O expenses to be repaid by RMC to members’ capital on scheduled redemptions. The amounts credited were determined by the ratio between the amount of the formation loan and the amount of offering costs incurred by the company. The change in 2022 has no net effect on the amounts paid by RMC to RMI IX.