Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2014
Accounting Policies [Abstract]
Organization [Text Block]	Organization Dynex Capital, Inc., ("Company”) was incorporated in the Commonwealth of Virginia on December 18, 1987 and commenced operations in February 1988. The Company primarily earns income from investing on a leveraged basis in mortgage-backed securities ("MBS") that are issued or guaranteed by the U.S. Government or U.S. Government sponsored agencies ("Agency MBS") and MBS issued by others ("non-Agency MBS").
Basis of Presentation [Policy Text Block]	Basis of Presentation The accompanying consolidated financial statements of Dynex Capital, Inc. and its qualified real estate investment trust ("REIT") subsidiaries and its taxable REIT subsidiary (together, "Dynex" or the "Company") have been prepared in accordance with the generally accepted accounting principles in the United States ("GAAP") and the instructions to the Annual Report on Form 10-K and Article 3 of Regulation S-X promulgated by the Securities and Exchange Commission (the "SEC").
Reclassifications [Policy Text Block]	Reclassifications Certain items in the prior periods' consolidated financial statements have been reclassified to conform to the current year’s presentation. The Company's consolidated balance sheet as of December 31, 2013 now presents its "securitized mortgage loans, net" and "other investments, net" together as "mortgage loans held for investment, net ". In addition, the Company has combined the presentation of its consolidated statements of income and its consolidated statements of other comprehensive income together as one financial statement which is now titled "consolidated statements of comprehensive income". The Company's "interest income - securitized mortgage loans" and "interest income-other investments" on its consolidated statements of income for the years ended December 31, 2013 and December 31, 2012 are now presented together as "interest income-mortgage loans held for investment, net" on its consolidated statements of comprehensive income for the years ended December 31, 2013 and December 31, 2012. The Company's "amortization and depreciation" on its consolidated statements of cash flows for the years ended December 31, 2013 and December 31, 2012 are now presented as "amortization of investment premiums, net" and "other amortization and depreciation". These presentation changes have no effect on reported total assets, total liabilities, results of operations, or cash flow activities.
Consolidation [Policy Text Block]	Consolidation The consolidated financial statements include the accounts of the Company and the accounts of its majority owned subsidiaries and variable interest entities ("VIE") for which it is the primary beneficiary. As a primary beneficiary, the Company has both the power to direct the activities that most significantly impact the economic performance of the VIE and a right to receive benefits or absorb losses of the entity that could be potentially significant to the VIE. The Company is required to reconsider its evaluation of whether to consolidate a VIE each reporting period, based upon changes in the facts and circumstances pertaining to the VIE. All intercompany accounts and transactions have been eliminated in consolidation. The Company consolidates certain trusts through which it has securitized mortgage loans as a result of not meeting the sale criteria under GAAP at the time the financial assets were transferred to the trust. Additional information regarding the accounting policy for the Company's securitized mortgage loans is provided below under "Mortgage Loans Held for Investment, Net ".
Use of Estimates [Policy Text Block]	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements as well as the reported amounts of revenue and expenses during the reported period. Actual results could differ from those estimates. The most significant estimates used by management include, but are not limited to, fair value measurements of its investments, other-than-temporary impairments, contingencies, and amortization of premiums and discounts. These items are discussed further below within this note to the consolidated financial statements.
Federal Income Taxes [Policy Text Block]	Income Taxes The Company has elected to be taxed as a real estate investment trust ("REIT") under the Internal Revenue Code of 1986 and the corresponding provisions of state law. To qualify as a REIT, the Company must meet certain tests including investing in primarily real estate-related assets and the required distribution of at least 90% of its annual REIT taxable income to stockholders after consideration of its net operating loss carryforward and not including taxable income retained in its taxable subsidiaries. As a REIT, the Company generally will not be subject to federal income tax on the amount of its income or gain that is distributed as dividends to shareholders. The Company assesses its tax positions for all open tax years and determines whether the Company has any material unrecognized liabilities in accordance with ASC Topic 740. The Company records these liabilities, if any, to the extent they are deemed more likely than not to have been incurred.
Cash and Cash Equivalents, Policy [Policy Text Block]	Cash and Cash Equivalents Cash and cash equivalents include cash on hand and highly liquid investments with original maturities of three months or less.
Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block]	Restricted Cash Restricted cash consists of cash the Company has pledged to cover initial and variation margin with its counterparties.
Mortgage Backed Securities [Policy Text Block]	Mortgage-Backed Securities In accordance with ASC Topic 320, the Company has designated its investments in MBS as available-for-sale ("AFS"). All of the Company’s MBS are recorded at fair value on the consolidated balance sheet. Changes in fair value for the Company's AFS securities are reported in other comprehensive income ("OCI") until each security is collected, disposed of, or determined to be other than temporarily impaired. Although the Company generally intends to hold its AFS securities until maturity, it may sell any of these securities as part of the overall management of its business. Upon the sale of an AFS security, any unrealized gain or loss is reclassified out of accumulated other comprehensive income ("AOCI") into net income as a realized "gain (loss) on sale of investments, net" using the specific identification method. The Company’s MBS pledged as collateral against repurchase agreements and derivative instruments are included in MBS on the consolidated balance sheets with the fair value of the MBS pledged disclosed parenthetically. Interest Income, Premium Amortization, and Discount Accretion. Interest income on MBS is accrued based on the outstanding principal balance (or notional balance in the case of interest-only, or "IO", securities) and their contractual terms. Premiums and discounts on Agency MBS as well as any non-Agency MBS rated 'AA' and higher at the time of purchase are amortized into interest income over the expected life of such securities using the effective yield method and adjustments to premium amortization are made for actual cash payments as well as changes in projected future cash payments in accordance with ASC Topic 310-20. The Company's projections of future cash payments are based on input and analysis received from external sources and internal models, and includes assumptions about the amount and timing of credit losses, loan prepayment rates, fluctuations in interest rates, and other factors. On at least a quarterly basis, the Company reviews and makes any necessary adjustments to its cash flow projections and updates the yield recognized on these assets. The Company holds non-Agency MBS that were rated less than 'AA' at the time of purchase by at least one national rating agency. These non-Agency MBS were purchased at discounts to their par value, which management does not believe to be substantial. The Company accretes the discount into income over the security's expected life, which reflects management's estimate of the security's projected cash flows in accordance with ASC Topic 325-40. Future changes in the timing of projected cash flows or differences arising between projected cash flows and actual cash flows received may result in a prospective change in the effective yield on those securities. Determination of MBS Fair Value. The Company estimates the fair value of the majority of its MBS based upon prices obtained from third-party pricing services and broker quotes. The remainder of the Company's MBS are valued by discounting the estimated future cash flows derived from cash flow models that utilize information such as the security's coupon rate, estimated prepayment speeds, expected weighted average life, collateral composition, estimated future interest rates, expected losses, and credit enhancements as well as certain other relevant information. Refer to Note 8 for further discussion of MBS fair value measurements. Other-than-Temporary Impairment. MBS is considered impaired when its fair value is less than its amortized cost. The Company evaluates all of its impaired MBS for other-than-temporary impairments ("OTTI") on at least a quarterly basis. An impairment is considered other-than-temporary if: (1) the Company intends to sell the MBS; (2) it is more likely than not that the Company will be required to sell the MBS before its fair value recovers; or (3) the Company does not expect to recover the full amortized cost basis of the MBS. If either of the first two conditions is met, the entire amount of the impairment is recognized in earnings. If the impairment is solely due to the inability to fully recover the amortized cost basis, the security is further analyzed to quantify any credit loss, which is the difference between the present value of cash flows expected to be collected on the MBS and its amortized cost. The credit loss, if any, is then recognized in earnings, while the balance of impairment related to other factors is recognized in other comprehensive income. Following the recognition of an OTTI through earnings, a new cost basis is established for the security. Any subsequent recoveries in fair value may be accreted back into the amortized cost basis of the MBS on a prospective basis through interest income. Please see Note 3 for additional information related to the Company's evaluation for OTTI.
Mortgage Loans Held for Investment, Net [Policy Text Block]	Mortgage Loans Held for Investment, Net The Company originated or purchased mortgage loans from 1992 through 1998, and these mortgage loans are reported at amortized cost in accordance with ASC Topic 310-10. A portion of these loans is pledged as collateral to support the repayment of one remaining class of a securitization financing bond issued by the Company in 2002. The associated securitization financing bond is treated as debt of the Company and is presented as "non-recourse collateralized financing" on the consolidated balance sheet. Securitized mortgage loans can only be sold subject to the lien of the respective securitization financing indenture. An allowance has been established for currently existing and probable losses on the Company's mortgage loans held for investment.
Investment in Limited Partnership [Policy Text Block]	Investment in Limited Partnership The Company is a limited partner with a less than 50% interest in a limited partnership for which it does not have substantive participating or kick-out rights that overcome the general partner's presumption of control. The Company accounts for its investment in this limited partnership using the equity method of accounting, which requires initially recording an investment in the equity of an investee at cost and subsequently adjusting the carrying amount of the investment to recognize the investor's share of the earnings or losses, capital contributions and distributions, and other changes in equity.
Repurchase Agreements [Policy Text Block]	Repurchase Agreements Repurchase agreements are accounted for as secured borrowings under which the Company pledges its securities as collateral to secure a loan, which is equal in value to a specified percentage of the estimated fair value of the pledged collateral. The Company retains beneficial ownership of the pledged collateral. At the maturity of a repurchase agreement, the Company is required to repay the loan and concurrently receives back its pledged collateral from the lender or, with the consent of the lender, the Company may renew the agreement at the then prevailing financing rate. A repurchase agreement lender may require the Company to pledge additional collateral in the event of a decline in the fair value of the collateral pledged. Repurchase agreement financing is recourse to the Company and the assets pledged. Most of the Company’s repurchase agreements are based on the September 1996 version of the Bond Market Association Master Repurchase Agreement, which generally provides that the lender, as buyer, is responsible for obtaining collateral valuations from a generally recognized source agreed to by both the Company and the lender, or, in an instance when such source is not available, the value determination is made by the lender.
Derivative Instruments [Policy Text Block]	Derivative Instruments The Company's derivative instruments, which currently include interest rate swaps and Eurodollar futures, are accounted for in accordance with ASC Topic 815, which requires an entity to recognize all derivatives as either assets or liabilities in the balance sheet and to measure those instruments at fair value. All periodic interest costs and other changes in fair value, including gains and losses recognized upon termination, associated with derivative instruments are recorded in "gain (loss) on derivative instruments, net" on the Company's consolidated statement of comprehensive income. Effective June 30, 2013, the Company discontinued cash flow hedge accounting for derivative instruments which had previously been accounted for as cash flow hedges under ASC Topic 815. Activity up to and including June 30, 2013 for those agreements previously designated as cash flow hedges was recorded in accordance with cash flow hedge accounting as prescribed by ASC Topic 815, which states that the effective portion of the hedge relationship on an instrument designated as a cash flow hedge is reported in the current period's other comprehensive income while the ineffective portion is immediately reported as a component of the current period’s net income. The balance remaining in AOCI related to the de-designated cash flow hedges is amortized into the Company's net income as a portion of "interest expense" over the remaining life of the interest rate swap agreements. Subsequent to June 30, 2013, changes in the fair value of the Company's derivative instruments, plus periodic settlements, are recorded in the Company's net income as a portion of "gain (loss) on derivative instruments, net". Although MBS have characteristics that meet the definition of a derivative instrument, ASC Topic 815 specifically excludes these instruments from its scope because they are accounted for as debt securities under ASC Topic 320.
Stock-based Compensation [Policy Text Block]	Share-Based Compensation Pursuant to the Company’s 2009 Stock and Incentive Plan ("SIP"), the Company may grant share-based compensation to eligible employees, directors or consultants or advisers to the Company, including stock awards, stock options, stock appreciation rights, dividend equivalent rights, performance shares, and restricted stock units. The Company's restricted stock currently issued and outstanding under this plan may be settled only in shares of its common stock, and therefore are treated as equity awards with their fair value measured at the grant date and recognized as compensation cost over the requisite service period with a corresponding credit to shareholders' equity. The requisite service period is the period during which an employee is required to provide service in exchange for an award, which is equivalent to the vesting period specified in the terms of the share-based based award. None of the Company's restricted stock awards have performance based conditions. The Company does not currently have any share-based compensation issued or outstanding other than restricted stock.
Contingencies [Policy Text Block]	Contingencies In the normal course of business, there are various lawsuits, claims, and other contingencies pending against the Company. On a quarterly basis, the Company evaluates whether to establish provisions for estimated losses from those matters in accordance with ASC Topic 450, which states that a liability is recognized for a contingent loss when: (a) the underlying causal event has occurred prior to the balance sheet date; (b) it is probable that a loss has been incurred; and (c) there is a reasonable basis for estimating that loss. A liability is not recognized for a contingent loss when it is only possible or remotely possible that a loss has been incurred, however, possible contingent losses shall be disclosed. If the contingent loss (or an additional loss in excess of any accrual) is at least a reasonable possibility and material, then the Company discloses a reasonable estimate of the possible loss or range of loss, if such reasonable estimate can be made. If the Company cannot make a reasonable estimate of the possible material loss, or range of loss, then that fact is disclosed. As of December 31, 2014, the Company does not have any contingencies for which it believes a probable loss has been incurred.
Recent Accounting Pronouncements [Text Block]	Recent Accounting Pronouncements In June 2014, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2014-11, Transfers and Servicing (Topic 860): Repurchase-to-Maturity Transactions, Repurchase Financings, and Disclosures, which changes the accounting for repurchase-to-maturity transactions and repurchase financing arrangements. The guidance eliminates sale accounting for repurchase-to-maturity transactions and supersedes the guidance under which a transfer of a financial asset and a contemporaneous repurchase financing could be accounted for on a combined basis as a forward agreement, which has resulted in outcomes referred to as off-balance-sheet accounting. All of the Company's repurchase agreement transactions are accounted for as secured borrowings; therefore the accounting changes required by ASU No. 2014-11 do not impact the Company's consolidated financial statements. ASU No. 2014-11 also requires two additional disclosures about repurchase agreements and other similar transactions. The first disclosure requires an entity to disclose information on transfers accounted for as sales in transactions that are economically similar to repurchase agreements. The Company does not account for any of its repurchase agreement transactions as sales; therefore this new disclosure does not impact the Company's current disclosures. The second disclosure requires the following disclosures for repurchase agreements, securities lending transactions, and repurchase-to-maturity transactions that are accounted for as secured borrowings: a disaggregation of the gross obligation by the class of collateral pledged; the remaining contractual tenor of the agreements; and a discussion of the potential risks associated with the agreements and the related collateral pledged, including obligations arising from a decline in the fair value of the collateral pledged and how those risks are managed. The Company already provides these disclosures in its "Notes to the Consolidated Financial Statements" and within "Liquidity and Capital Resources" in Item 7, "Management's Discussion and Analysis of Financial Condition and Results of Operations" of this Annual Report on Form 10-K. The amendments provided in ASU No. 2014-11 are effective for public business entities for the first interim or annual period beginning after December 15, 2014. ASU No. 2014-11 will not have a material impact on the Company's consolidated financial statements. In addition, the FASB issued ASU No. 2014-12, Compensation - Stock Compensation (Topic 718): Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period. The amendments in this ASU are effective for annual periods and interim periods within those annual periods beginning after December 15, 2015. The Company has not issued and does not anticipate issuing any share-based payments with terms that require a performance-based target; therefore this ASU will not have an impact on the Company's consolidated financial statements. The FASB issued ASU No. 2014-13, Consolidation (Topic 810): Measuring the Financial Assets and the Financial Liabilities of a Consolidated Collateralized Financing Entity, which provides an alternative to Topic 820, Fair Value Measurement, for measuring the financial assets and the financial liabilities of a consolidated collateralized financing entity to eliminate the difference in the fair value of the financial assets of a collateralized financing entity, as determined under GAAP, when they differ from the fair value of its financial liabilities even when the financial liabilities have recourse only to the financial assets. When the measurement alternative is elected, both the financial assets and the financial liabilities of the collateralized financing entity should be measured using the more observable of the fair value of the financial assets or the fair value of the financial liabilities. The amendments clarify that when the measurement alternative is elected, a reporting entity's consolidated net income (loss) should reflect the reporting entity's own economic interests in the collateralized financing entity, including; (1) changes in the fair value of the beneficial interests retained by the reporting entity, and (2) beneficial interests that represent compensation for services. The measurement alternative provided in ASU No. 2014-13 may be applied using a modified retrospective approach by recording a cumulative-effect adjustment to equity as of the beginning of the annual period of adoption. The amendments may also be applied retrospectively to all relevant prior periods beginning with the annual period in which ASU No. 2009-17 was initially adopted. ASU No. 2014-13 is effective for public entities for annual periods, and interim periods within those annual periods, beginning after December 15, 2015, and early adoption is permitted as of the beginning of an annual period. Management has evaluated ASU No. 2014-13 and has determined that if the Company elects to adopt this measurement alternative in the future for its currently existing consolidated collateralized financing entity, it will not have a material impact on the Company's consolidated financial statements. The FASB issued ASU No. 2014-15, Presentation of Financial Statements-Going Concern (Subtopic 205-40): Disclosure of Uncertainties about an Entity's Ability to Continue as a Going Concern, which provides guidance about management's responsibility under GAAP to evaluate whether there is substantial doubt about an organization's ability to continue as a going concern and to provide related footnote disclosures. Specifically, the ASU (1) provides a definition of the term "substantial doubt", (2) requires an evaluation by management every reporting period including interim periods, (3) provides principles for considering the mitigating effect of management's plans, (4) requires certain disclosures when substantial doubt exists regardless of the success of any mitigating plans or actions, (5) requires an express statement and other disclosures when substantial doubt is not alleviated, and (6) requires an assessment for a period of one year after the date that the financial statements are issued. The amendments in this ASU are effective for the annual period ending after December 15, 2016, and for annual periods and interim periods thereafter. Early application is permitted. Management intends to comply with the requirements set forth in ASU No. 2014-15.