Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2017
Accounting Policies [Abstract]
Basis of Presentation	The consolidated financial statements presented herein are at September 30, 2017 and December 31, 2016, and for the three and nine months ended September 30, 2017 and 2016. 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, 2016. In the opinion of management, all normal and recurring adjustments to present fairly the financial condition of the company at September 30, 2017 and results of operations for all periods presented have been made. The results of operations for the three and nine months ended September 30, 2017 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 where we maintain an ongoing involvement ("Legacy Sequoia"), as well as an entity formed in connection with the securitization of Redwood Choice expanded-prime loans during the third quarter of 2017 ("Sequoia Choice"). 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, servicing 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 entities are shown under Residential loans, held-for-investment, 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, we recorded interest income on the loans 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 January 2017, the FASB issued ASU 2017-03, "Accounting Changes and Error Corrections (Topic 250) and Investments - Equity Method and Joint Ventures (Topic 323)." This new guidance requires that companies evaluate ASUs that have not been adopted to determine the appropriate financial statement disclosures about the potential material effects of those ASUs on the financial statements when adopted. This new guidance was effective immediately. We adopted this guidance, as required, in the first quarter of 2017, 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 provides simplifications of 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 August 2017, the FASB issued ASU 2017-12, "Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities." This new guidance amends previous guidance to better align an entity's risk management activities and financial reporting for hedging relationships through changes to both the designation and measurement guidance for qualifying hedging relationships and the presentation of hedge results. 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 July 2017, the FASB issued ASU 2017-11, "Earnings Per Share (Topic 260); Distinguishing Liabilities from Equity (Topic 480); Derivatives and Hedging (Topic 815): (Part I) Accounting for Certain Financial Instruments with Down Round Features, (Part II) Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception." This new guidance changes the classification analysis of certain equity-linked financial instruments (or embedded conversion options) with down round features. 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 do not anticipate that this update will have a material impact on our consolidated financial statements. In March 2017, the FASB issued ASU 2017-08, "Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20)." This new guidance shortens the amortization period for certain callable debt securities purchased at a premium by requiring the premium to be amortized to the earliest call date. 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 do not anticipate that this update will have a material impact on our consolidated financial statements. In November 2016, the FASB issued ASU 2016-18, "Statement of Cash Flows (Topic 230): Restricted Cash." This new guidance amends previous guidance on how to classify and present changes in restricted cash on 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 will modify the presentation of our cash flow statement as required. 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 do not anticipate that this update will have a material impact 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 do not anticipate that this update will have a material impact 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 years beginning December 15, 2018. Currently, a significant portion of our financial instruments are measured at fair value, for which we do not maintain any allowances for loan losses in accordance with fair value accounting. As such, based on our initial evaluation of this new guidance, we do not believe the provisions in this guidance will have a material impact to how we account for these instruments. Separately, we account for our available-for-sale securities under the other-than-temporary impairment ("OTTI") model for debt securities. This new guidance changes the accounting for available-for-sale securities, including AFS securities purchased with credit deterioration. We are currently evaluating the impact that this update will have on our consolidated financial statements in regard to our available-for-sale securities. We plan to adopt this new guidance by the required date. 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. As discussed in Note 14, our only material leases are those related to our leased office space, for which future payments under these leases total $18 million at September 30, 2017. Upon adoption of this standard in the first quarter of 2019, we will record a right-of-use asset and lease liability equal to the present value of these future lease payments discounted at our incremental borrowing rate. Based on our initial evaluation of this new guidance, and taking into consideration our current in-place leases, we do not expect that its adoption will have a material impact on our consolidated financial statements. We will continue evaluating this new standard and caution that any changes in our business or additional leases we may enter into could change our initial assessment. 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 do not anticipate that this update will have a material impact 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," and in December 2016, the FASB issued ASU 2016-20, "Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers." These new ASUs provide more specific guidance on certain aspects of Topic 606. In September 2017, the FASB issued ASU 2017-13, "Revenue Recognition (Topic 605), Revenue from Contracts with Customers (Topic 606), Leases (Topic 840), and Leases (Topic 842): Amendments to SEC Paragraphs Pursuant to the Staff Announcement at the July 20, 2017 EITF Meeting and Rescission of Prior SEC Staff Announcements and Observer Comments (SEC Update). This new ASU allows certain public business entities to use the nonpublic business entity effective dates for adoption of the new revenue standard. Based on our initial evaluation of these new accounting standards, we do not expect that their adoption will have a material impact on our consolidated financial statements, as financial instruments are explicitly scoped out of the standards and nearly all of our income is generated from financial instruments. We will continue evaluating these new standards and caution that any changes in our business or additional amendments to these standards could change our initial assessment.
Balance Sheet Netting	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. 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.