Summary of Significant Accounting Policies (Policies)	9 Months Ended
Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of PresentationThe consolidated financial statements presented herein are at September 30, 2021 and December 31, 2020, and for the three and nine months ended September 30, 2021 and 2020. These interim unaudited consolidated financial statements have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission ("SEC"). Certain information and note disclosures normally included in our annual financial statements prepared in accordance with U.S. generally accepted accounting principles ("GAAP") — as prescribed by the Financial Accounting Standards Board’s (“FASB”) Accounting Standards Codification (“ASC”) — have been condensed or omitted in these interim financial statements according to these SEC rules and regulations. Management believes that the disclosures included in these interim financial statements should be read in conjunction with the consolidated financial statements and notes thereto included in the company's Annual Report on Form 10-K for the year ended December 31, 2020. In the opinion of management, all normal and recurring adjustments to present fairly the financial condition of the Company at September 30, 2021 and results of operations for all periods presented have been made. The results of operations for the three and nine months ended September 30, 2021 should not be construed as indicative of the results to be expected for the full year.
Principles of Consolidation	Principles of Consolidation In accordance with GAAP, we determine whether we must consolidate transferred financial assets and variable interest entities (“VIEs”) for financial reporting purposes. We currently consolidate the assets and liabilities of certain Sequoia securitization entities issued prior to 2012 ("Legacy Sequoia"), certain entities formed during and after 2012 in connection with the securitization of Redwood Select prime loans and Redwood Choice expanded-prime loans ("Sequoia"), entities formed in connection with the securitization of CoreVest single-family rental and bridge loans ("CAFL"), and beginning in the third quarter of 2021, an entity ("Point HEI") formed in connection with the securitization of home equity investment contracts ("HEIs"). We also consolidate the assets and liabilities of certain Freddie Mac K-Series and Freddie Mac Seasoned Loans Structured Transaction ("SLST") securitizations in which we have invested. Each securitization entity is independent of Redwood and of each other and the assets and liabilities are not owned by and are not legal obligations of Redwood Trust, Inc. Our exposure to these entities is primarily through the financial interests we have purchased or retained, although for certain entities we are exposed to financial risks associated with our role as a sponsor or co-sponsor, servicing administrator, collateral administrator, or depositor of these entities or as a result of our having sold assets directly or indirectly to these entities. For financial reporting purposes, the underlying loans owned at the consolidated Sequoia and Freddie Mac SLST entities are shown under Residential loans held-for-investment at fair value, the underlying loans at the consolidated Freddie Mac K-Series entity are shown under Multifamily loans held-for-investment at fair value, the underlying single-family rental and bridge loans at the consolidated CAFL entities are shown under Business purpose loans held-for-investment at fair value, and the underlying HEIs at the consolidated Point HEI entity are shown under Other investments at fair value on our consolidated balance sheets. The asset-backed securities (“ABS”) issued to third parties by these entities are shown under ABS issued. In our consolidated statements of income (loss), we recorded interest income on the loans owned at these entities and interest expense on the ABS issued by these entities as well as fair value changes, other income and expenses associated with these entities' activities.
Use of Estimates	Use of Estimates The preparation of financial statements requires us to make a number of significant estimates. These include estimates of fair value of certain assets and liabilities, amounts and timing of credit losses, prepayment rates, and other estimates that affect the reported amounts of certain assets and liabilities as of the date of the consolidated financial statements and the reported amounts of certain revenues and expenses during the reported periods. It is likely that changes in these estimates (e.g., valuation changes due to supply and demand, credit performance, prepayments, interest rates, or other reasons) will occur in the near term. Our estimates are inherently subjective in nature and actual results could differ from our estimates and the differences could be material.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Newly Adopted Accounting Standards Updates ("ASUs") In August 2021, the FASB issued ASU 2021-06, "Presentation of Financial Statements (Topic 205), Financial Services—Depository and Lending (Topic 942), and Financial Services—Investment Companies (Topic 946): Amendments to SEC Paragraphs Pursuant to SEC Final Rule Releases No. 33-10786, Amendments to Financial Disclosures about Acquired and Disposed Businesses, and No. 33-10835, Update of Statistical Disclosures for Bank and Savings and Loan Registrants (SEC Update)." This new guidance aligns certain SEC paragraphs in the codification with new SEC rules issued in May 2020 related to changes to the disclosure requirements for acquired and disposed businesses. We adopted this guidance upon issuance in the third quarter of 2021, which did not have a material impact on our consolidated financial statements. In October 2020, the FASB issued ASU 2020-10, "Codification Improvements." This new guidance updates various codification topics by clarifying or improving disclosure requirements. This new guidance is effective for fiscal years ending after December 15, 2020. We adopted this guidance, as required, in the first quarter of 2021, which did not have a material impact on our consolidated financial statements. In October 2020, the FASB issued ASU 2020-09, "Debt (Topic 470): Amendments to SEC Paragraphs Pursuant to SEC Release No. 33-10762." This new guidance aligns certain SEC paragraphs in the codification with new SEC rules issued in March 2020 related to changes to the disclosure requirements for registered debt securities. This new guidance became effective January 4, 2021. We adopted this guidance, as required, in the first quarter of 2021, which did not have a material impact on our consolidated financial statements. In October 2020, the FASB issued ASU 2020-08, "Codification Improvements to Subtopic 310-20, Receivables - Nonrefundable Fees and Other Costs." This new guidance clarifies that an entity should reevaluate whether a callable debt security is within the scope of paragraph 310-20-35-33 for each reporting period. This new guidance is effective for fiscal years ending after December 15, 2020. We adopted this guidance, as required, in the first quarter of 2021, which did not have a material impact on our consolidated financial statements. In January 2020, the FASB issued ASU 2020-01, "Investments - Equity Securities (Topic 321), Investments - Equity Method and Joint Ventures (Topic 323), and Derivatives and Hedging (Topic 815)." This new guidance clarifies the interaction of the accounting for equity securities, equity method investments, and certain forward contracts and purchased options. This new guidance is effective for fiscal years beginning after December 15, 2020. We adopted this guidance, as required, in the first quarter of 2021, which did not have a material impact on our consolidated financial statements. In December 2019, the FASB issued ASU 2019-12, "Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes." This new guidance simplifies the accounting for income taxes by removing certain exceptions to the general principles in Topic 740 and by clarifying and amending existing guidance. This new guidance is effective for fiscal years beginning after December 15, 2020. We adopted this guidance, as required, in the first quarter of 2021, which did not have a material impact on our consolidated financial statements. Other Recent Accounting Pronouncements In August 2020, the FASB issued ASU 2020-06, "Debt - Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging - Contracts in Entity's Own Equity (Subtopic 815-40)." This new guidance simplifies the accounting for convertible debt by reducing the number of accounting models to separately present certain conversion features in equity. This new guidance is effective for fiscal years beginning after December 31, 2021. Early adoption is permitted. We plan to adopt this new guidance by the required date and do not anticipate that this update will have a material impact on our consolidated financial statements. In March 2020, the FASB issued ASU 2020-04, "Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting." This new guidance provides optional expedients and exceptions for applying GAAP to contracts, hedging relationships, and other transactions affected by reference rate reform if certain criteria are met. In January 2021, the FASB issued ASU 2021-01, "Reference Rate Reform (Topic 848): Scope." This new guidance clarifies that certain optional expedients and exceptions in Topic 848 for contract modifications and hedge accounting apply to derivatives that are affected by the discounting transition. This new guidance is effective for all entities as of March 12, 2020 through December 31, 2022. We are currently evaluating the impact the adoption of this standard would have on our consolidated financial statements. Through September 30, 2021, we have not elected to apply the optional expedients and exceptions to any of our existing contracts, hedging relationships, or other transactions.
Balance Sheet Netting	Balance Sheet Netting Certain of our derivatives and short-term debt are subject to master netting arrangements or similar agreements. Under GAAP, in certain circumstances we may elect to present certain financial assets, liabilities and related collateral subject to master netting arrangements in a net position on our consolidated balance sheets. However, we do not report any of these financial assets or liabilities on a net basis, and instead present them on a gross basis on our consolidated balance sheets.For each category of financial instrument set forth in the table above, the assets and liabilities resulting from individual transactions within that category between us and a counterparty are subject to a master netting arrangement or similar agreement with that counterparty that provides for individual transactions to be aggregated and treated as a single transaction. For certain categories of these instruments, some of our transactions are cleared and settled through one or more clearinghouses that are substituted as our counterparty. References herein to master netting arrangements or similar agreements include the arrangements and agreements governing the clearing and settlement of these transactions through the clearinghouses. In the event of the termination and close-out of any of those transactions, the corresponding master netting agreement or similar agreement provides for settlement on a net basis. Any such settlement would include the proceeds of the liquidation of any corresponding collateral, subject to certain limitations on termination, settlement, and liquidation of collateral that may apply in the event of the bankruptcy or insolvency of a party. Such limitations should not inhibit the eventual practical realization of the principal benefits of those transactions or the corresponding master netting arrangement or similar agreement and any corresponding collateral.

Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2021

Basis of PresentationThe consolidated financial statements presented herein are at September 30, 2021 and December 31, 2020, and for the three and nine months ended September 30, 2021 and 2020. These interim unaudited consolidated financial statements have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission ("SEC"). Certain information and note disclosures normally included in our annual financial statements prepared in accordance with U.S. generally accepted accounting principles ("GAAP") — as prescribed by the Financial Accounting Standards Board’s (“FASB”) Accounting Standards Codification (“ASC”) — have been condensed or omitted in these interim financial statements according to these SEC rules and regulations. Management believes that the disclosures included in these interim financial statements should be read in conjunction with the consolidated financial statements and notes thereto included in the company's Annual Report on Form 10-K for the year ended December 31, 2020. In the opinion of management, all normal and recurring adjustments to present fairly the financial condition of the Company at September 30, 2021 and results of operations for all periods presented have been made. The results of operations for the three and nine months ended September 30, 2021 should not be construed as indicative of the results to be expected for the full year.

Principles of Consolidation

In accordance with GAAP, we determine whether we must consolidate transferred financial assets and variable interest entities (“VIEs”) for financial reporting purposes. We currently consolidate the assets and liabilities of certain Sequoia securitization entities issued prior to 2012 ("Legacy Sequoia"), certain entities formed during and after 2012 in connection with the securitization of Redwood Select prime loans and Redwood Choice expanded-prime loans ("Sequoia"), entities formed in connection with the securitization of CoreVest single-family rental and bridge loans ("CAFL"), and beginning in the third quarter of 2021, an entity ("Point HEI") formed in connection with the securitization of home equity investment contracts ("HEIs"). We also consolidate the assets and liabilities of certain Freddie Mac K-Series and Freddie Mac Seasoned Loans Structured Transaction ("SLST") securitizations in which we have invested. Each securitization entity is independent of Redwood and of each other and the assets and liabilities are not owned by and are not legal obligations of Redwood Trust, Inc. Our exposure to these entities is primarily through the financial interests we have purchased or retained, although for certain entities we are exposed to financial risks associated with our role as a sponsor or co-sponsor, servicing administrator, collateral administrator, or depositor of these entities or as a result of our having sold assets directly or indirectly to these entities.

For financial reporting purposes, the underlying loans owned at the consolidated Sequoia and Freddie Mac SLST entities are shown under Residential loans held-for-investment at fair value, the underlying loans at the consolidated Freddie Mac K-Series entity are shown under Multifamily loans held-for-investment at fair value, the underlying single-family rental and bridge loans at the consolidated CAFL entities are shown under Business purpose loans held-for-investment at fair value, and the underlying HEIs at the consolidated Point HEI entity are shown under Other investments at fair value on our consolidated balance sheets. The asset-backed securities (“ABS”) issued to third parties by these entities are shown under ABS issued. In our consolidated statements of income (loss), we recorded interest income on the loans owned at these entities and interest expense on the ABS issued by these entities as well as fair value changes, other income and expenses associated with these entities' activities.

Use of Estimates

The preparation of financial statements requires us to make a number of significant estimates. These include estimates of fair value of certain assets and liabilities, amounts and timing of credit losses, prepayment rates, and other estimates that affect the reported amounts of certain assets and liabilities as of the date of the consolidated financial statements and the reported amounts of certain revenues and expenses during the reported periods. It is likely that changes in these estimates (e.g., valuation changes due to supply and demand, credit performance, prepayments, interest rates, or other reasons) will occur in the near term. Our estimates are inherently subjective in nature and actual results could differ from our estimates and the differences could be material.

Recent Accounting Pronouncements

Newly Adopted Accounting Standards Updates ("ASUs")

In August 2021, the FASB issued ASU 2021-06, "Presentation of Financial Statements (Topic 205), Financial Services—Depository and Lending (Topic 942), and Financial Services—Investment Companies (Topic 946): Amendments to SEC Paragraphs Pursuant to SEC Final Rule Releases No. 33-10786, Amendments to Financial Disclosures about Acquired and Disposed Businesses, and No. 33-10835, Update of Statistical Disclosures for Bank and Savings and Loan Registrants (SEC Update)." This new guidance aligns certain SEC paragraphs in the codification with new SEC rules issued in May 2020 related to changes to the disclosure requirements for acquired and disposed businesses. We adopted this guidance upon issuance in the third quarter of 2021, which did not have a material impact on our consolidated financial statements.

In October 2020, the FASB issued ASU 2020-10, "Codification Improvements." This new guidance updates various codification topics by clarifying or improving disclosure requirements. This new guidance is effective for fiscal years ending after December 15, 2020. We adopted this guidance, as required, in the first quarter of 2021, which did not have a material impact on our consolidated financial statements.

In October 2020, the FASB issued ASU 2020-09, "Debt (Topic 470): Amendments to SEC Paragraphs Pursuant to SEC Release No. 33-10762." This new guidance aligns certain SEC paragraphs in the codification with new SEC rules issued in March 2020 related to changes to the disclosure requirements for registered debt securities. This new guidance became effective January 4, 2021. We adopted this guidance, as required, in the first quarter of 2021, which did not have a material impact on our consolidated financial statements.

In October 2020, the FASB issued ASU 2020-08, "Codification Improvements to Subtopic 310-20, Receivables - Nonrefundable Fees and Other Costs." This new guidance clarifies that an entity should reevaluate whether a callable debt security is within the scope of paragraph 310-20-35-33 for each reporting period. This new guidance is effective for fiscal years ending after December 15, 2020. We adopted this guidance, as required, in the first quarter of 2021, which did not have a material impact on our consolidated financial statements.

In January 2020, the FASB issued ASU 2020-01, "Investments - Equity Securities (Topic 321), Investments - Equity Method and Joint Ventures (Topic 323), and Derivatives and Hedging (Topic 815)." This new guidance clarifies the interaction of the accounting for equity securities, equity method investments, and certain forward contracts and purchased options. This new guidance is effective for fiscal years beginning after December 15, 2020. We adopted this guidance, as required, in the first quarter of 2021, which did not have a material impact on our consolidated financial statements.

In December 2019, the FASB issued ASU 2019-12, "Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes." This new guidance simplifies the accounting for income taxes by removing certain exceptions to the general principles in Topic 740 and by clarifying and amending existing guidance. This new guidance is effective for fiscal years beginning after December 15, 2020. We adopted this guidance, as required, in the first quarter of 2021, which did not have a material impact on our consolidated financial statements.

Other Recent Accounting Pronouncements

In August 2020, the FASB issued ASU 2020-06, "Debt - Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging - Contracts in Entity's Own Equity (Subtopic 815-40)." This new guidance simplifies the accounting for convertible debt by reducing the number of accounting models to separately present certain conversion features in equity. This new guidance is effective for fiscal years beginning after December 31, 2021. Early adoption is permitted. We plan to adopt this new guidance by the required date and do not anticipate that this update will have a material impact on our consolidated financial statements.

In March 2020, the FASB issued ASU 2020-04, "Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting." This new guidance provides optional expedients and exceptions for applying GAAP to contracts, hedging relationships, and other transactions affected by reference rate reform if certain criteria are met. In January 2021, the FASB issued ASU 2021-01, "Reference Rate Reform (Topic 848): Scope." This new guidance clarifies that certain optional expedients and exceptions in Topic 848 for contract modifications and hedge accounting apply to derivatives that are affected by the discounting transition. This new guidance is effective for all entities as of March 12, 2020 through December 31, 2022. We are currently evaluating the impact the adoption of this standard would have on our consolidated financial statements. Through September 30, 2021, we have not elected to apply the optional expedients and exceptions to any of our existing contracts, hedging relationships, or other transactions.

Balance Sheet Netting

Balance Sheet Netting Certain of our derivatives and short-term debt are subject to master netting arrangements or similar agreements. Under GAAP, in certain circumstances we may elect to present certain financial assets, liabilities and related collateral subject to master netting arrangements in a net position on our consolidated balance sheets. However, we do not report any of these financial assets or liabilities on a net basis, and instead present them on a gross basis on our consolidated balance sheets.For each category of financial instrument set forth in the table above, the assets and liabilities resulting from individual transactions within that category between us and a counterparty are subject to a master netting arrangement or similar agreement with that counterparty that provides for individual transactions to be aggregated and treated as a single transaction. For certain categories of these instruments, some of our transactions are cleared and settled through one or more clearinghouses that are substituted as our counterparty. References herein to master netting arrangements or similar agreements include the arrangements and agreements governing the clearing and settlement of these transactions through the clearinghouses. In the event of the termination and close-out of any of those transactions, the corresponding master netting agreement or similar agreement provides for settlement on a net basis. Any such settlement would include the proceeds of the liquidation of any corresponding collateral, subject to certain limitations on termination, settlement, and liquidation of collateral that may apply in the event of the bankruptcy or insolvency of a party. Such limitations should not inhibit the eventual practical realization of the principal benefits of those transactions or the corresponding master netting arrangement or similar agreement and any corresponding collateral.