Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2016
Accounting Policies [Abstract]
Basis of Presentation	The consolidated financial statements presented herein are at September 30, 2016 and December 31, 2015, and for the three and nine months ended September 30, 2016 and 2015. 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 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 according to these SEC rules and regulations. Management believes that the disclosures included in these interim financial statements should be read in conjunction with consolidated financial statements and notes thereto included in the company's Annual Report on Form 10-K for the year ended December 31, 2015. In the opinion of management, all normal and recurring adjustments to present fairly the financial condition of the company at September 30, 2016 and results of operations for all periods presented have been made. The results of operations for the three and nine months ended September 30, 2016 should not be construed as indicative of the results to be expected for the full year. In the second quarter of 2015, we began to specifically identify derivatives that are used to hedge our exposure to market interest rate risk associated with our mortgage servicing right ("MSR") investments. As a result, beginning in the second quarter of 2015, we changed our income statement presentation to include the change in market value of these derivatives in the line item “Mortgage servicing rights income (loss), net.” As we previously managed our market interest rate risk on a portfolio-wide basis and did not necessarily rely on derivatives to hedge our MSRs, we cannot conform prior periods to the current presentation. Therefore, in periods prior to the second quarter of 2015 presented in our consolidated statements of income, amounts in “Mortgage servicing rights income (loss), net” do not reflect the impact of hedging. These changes and year-over-year comparisons are discussed in further detail in Part I, Item 2, Management’s Discussion and Analysis of Financial Condition and Results of Operations in this Quarterly Report on Form 10-Q. Additionally, in the first quarter of 2016, we began to present the changes in fair value of certain investments and their associated derivatives in the new line item "Investment fair value changes, net" on our consolidated statements of income and began to present income from mortgage banking activities in "Mortgage banking activities, net" on our consolidated statements of income. We conformed the presentation of prior periods related to this change for consistency of comparison. See Notes 18 and 19 for additional detail on the components of these income statement line items.
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 where we maintain an ongoing involvement. From its creation in 2012 through the second quarter of 2016, when the third party financing was repaid, we consolidated the assets and liabilities of an entity formed in connection with a commercial securitization we engaged in (“Commercial Securitization”). We also consolidated the assets and liabilities of an entity formed in connection with a resecuritization transaction we engaged in (“Residential Resecuritization”) from its creation in 2011 through the fourth quarter of 2015, when the debt of the entity was repaid, the assets of the entity were distributed to us, and the entity was dissolved. 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 retained, although we are exposed to certain financial risks associated with our role as a sponsor, manager, 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 and securities owned at the consolidated Sequoia entities, the Residential Resecuritization entity, and the Commercial Securitization entity are shown under residential and commercial loans and real estate securities 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, we recorded interest income on the loans and securities owned at these entities and interest expense on the ABS issued by these entities as well as 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 April 2015, the FASB issued ASU 2015-05, “Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40): Customer's Accounting for Fees Paid in a Cloud-Computing Arrangement.” This new guidance provides additional guidance on accounting for fees paid in a cloud-computing arrangement that contains a software license. This new guidance is effective for fiscal years beginning after December 15, 2015. We adopted this guidance, as required, in the first quarter of 2016, which did not have a material impact on our consolidated financial statements. In April 2015, the FASB issued ASU 2015-03, “Simplifying the Presentation of Debt Issuance Costs.” This new guidance requires debt issuance costs to be presented in the balance sheet as a direct deduction from the carrying value of the associated debt liability, consistent with the presentation of a debt discount. This new guidance is effective for fiscal years beginning after December 15, 2015, and interim periods within those fiscal years, and is required to be applied on a retrospective basis. We adopted this guidance, as required, in the first quarter of 2016 and now present our deferred securities issuance costs as a reduction to the related liabilities on our consolidated balance sheets for all periods presented. At September 30, 2016 and December 31, 2015, we included zero and $0.5 million, respectively, of deferred securities issuance costs as a reduction to our ABS issued and presented these amounts together as ABS issued, net on our consolidated balance sheets and we included $8 million and $10 million, respectively, of deferred securities issuance costs as a reduction to our long-term debt and presented these amounts together as Long-term debt, net on our consolidated balance sheets. In February 2015, the FASB issued ASU 2015-02, “Consolidation (Topic 810) - Amendments to the Consolidation Analysis.” This new guidance provides a new scope exception for certain money market funds, makes targeted amendments to the current consolidation guidance, and ends the deferral granted to investment companies from applying the VIE guidance. This new guidance is effective for annual periods beginning after December 15, 2015. We adopted this guidance, as required, in the first quarter of 2016, which did not have a material impact on our consolidated financial statements. In March 2016, the FASB issued ASU 2016-09,"Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting." This new guidance is to simplify the accounting for share-based payment transactions, including related income tax accounting, classification of awards, and classification on the statement of cash flows. In addition, this guidance permits the withholding of employee taxes related to the distribution of equity awards up to the maximum individual employee statutory tax rates. This new guidance is effective for fiscal years beginning after December 15, 2016 and early adoption is permitted. In the second quarter of 2016, we adopted this new guidance. Upon adoption, we elected to account for forfeitures on employee equity awards as they occur, rather than estimating expected forfeitures. The adoption of this guidance did not have a material impact on our consolidated financial statements. Other Recent Accounting Pronouncements In October 2016, the FASB issued ASU 2016-17, "Consolidation (Topic 810): Interests Held Through Related Parties that Are Under Common Control." This new guidance amends the consolidation guidance on how a reporting entity, that is the single decision maker of a VIE, evaluates whether it is the primary beneficiary of a VIE. This new guidance is effective for fiscal years beginning after December 15, 2016. Early adoption is permitted. We plan to adopt this new guidance by the required date and we are currently evaluating the impact that this update will have on our consolidated financial statements. In October 2016, the FASB issued ASU 2016-16, "Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory." This new guidance allows an entity to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. It also eliminates the exceptions for an intra-entity transfer of assets other than inventory. This new guidance is effective for fiscal years beginning after December 15, 2017. Early adoption is permitted. We plan to adopt this new guidance by the required date and we are currently evaluating the impact that this update will have on our consolidated financial statements. In August 2016, the FASB issued ASU 2016-15, "Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments." This new guidance provides guidance on how to present and classify certain cash receipts and cash payments in the statement of cash flows. This new guidance is effective for fiscal years beginning after December 15, 2017. Early adoption is permitted. We plan to adopt this new guidance by the required date and we are currently evaluating the impact that this update will have on our consolidated financial statements. In June 2016, the FASB issued ASU 2016-13, "Financial Instruments - Credit Losses." This new guidance provides a new impairment model that is based on expected losses rather than incurred losses to determine the allowance for credit losses. This new guidance is effective for fiscal years beginning after December 15, 2019. Early adoption is permitted for fiscal year beginning December 15, 2018. We plan to adopt this new guidance by the required date and we are currently evaluating the impact that this update will have on our consolidated financial statements. In February 2016, the FASB issued ASU 2016-02,"Leases." This new guidance requires lessees to recognize most leases on their balance sheet as a right-of-use asset and a lease liability. This new guidance retains a dual lease accounting model, which requires leases to be classified as either operating or capital leases for lessees, for purposes of income statement recognition. This new guidance is effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. We plan to adopt this new guidance by the required date and we are currently evaluating the impact that this update will have on our consolidated financial statements. In January 2016, the FASB issued ASU 2016-01,"Recognition and Measurement of Financial Assets and Financial Liabilities." This new guidance amends accounting related to the classification and measurement of investments in equity securities and the presentation of certain fair value changes for financial liabilities measured at fair value. This new guidance also amends certain disclosure requirements associated with the fair value of financial instruments and it is effective for fiscal years beginning after December 15, 2017. We plan to adopt this new guidance by the required date and we are currently evaluating the impact that this update will have on our consolidated financial statements. In May 2014, the FASB issued ASU 2014-09, “Revenue from Contracts with Customers.” The update modifies the guidance companies use to recognize revenue from contracts with customers for transfers of goods or services and transfers of nonfinancial assets, unless those contracts are within the scope of other standards. The guidance also requires new qualitative and quantitative disclosures, including information about contract balances and performance obligations. In July 2015, the FASB approved a one year deferral of the effective date. Accordingly, the update is effective for us in the first quarter of 2018 with retrospective application to prior periods presented or as a cumulative effect adjustment in the period of adoption. Early adoption is permitted in the first quarter of 2017. In March 2016, the FASB issued ASU 2016-08, "Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (Reporting Revenue Gross versus Net)." This new guidance provides additional implementation guidance on how an entity should identify the unit of accounting for the principal versus agent evaluations. In May 2016, the FASB issued ASU 2016-12, "Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients." This new ASU provides more specific guidance on certain aspects of Topic 606. Based on our initial evaluation of this new accounting standard, we do not expect that its adoption will have a material impact on our consolidated financial statements, as financial instruments are explicitly scoped out of the standard and nearly all of our income is generated from financial instruments. We will continue evaluating this new standard and caution that any changes in our business or additional amendments to this standard could change our initial assessment.
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.