Organization and Investment Objective	12 Months Ended
Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Investment Objective	Organization and Investment Objective Ellington Residential Mortgage REIT, or "EARN," was formed as a Maryland real estate investment trust, or "REIT," on August 2, 2012, and commenced operations on September 25, 2012. EARN conducts its business through its wholly owned subsidiaries, EARN OP GP LLC, or the "General Partner," and Ellington Residential Mortgage LP, or the "Operating Partnership," which were formed as a Delaware limited liability company and a Delaware limited partnership, respectively, on July 31, 2012 and commenced operations on September 25, 2012. The Operating Partnership conducts its business of acquiring, investing in, and managing residential mortgage- and real estate-related assets through its wholly owned subsidiaries. EARN, the General Partner, the Operating Partnership, and their consolidated subsidiaries are hereafter defined as the "Company." Ellington Residential Mortgage Management LLC, or the "Manager," serves as the Manager of the Company pursuant to the terms of the Fifth Amended and Restated Management Agreement, or the "Management Agreement." The Manager is an affiliate of Ellington Management Group, L.L.C., or "EMG," an investment management firm that is an SEC-registered investment adviser with a 24-year history of investing in a broad spectrum of mortgage-backed securities and related derivatives, with an emphasis on the residential mortgage-backed securities, or "RMBS," market. In accordance with the terms of the Management Agreement and the Services Agreement (as described in Note 9), the Manager is responsible for administering the Company's business activities and day-to-day operations, and performs certain services, subject to oversight by the Board of Trustees. See Note 9 for further information on the Management Agreement. The Company acquires and manages RMBS, for which the principal and interest payments are guaranteed by a U.S. government agency or a U.S. government-sponsored entity, or "Agency RMBS," and RMBS that do not carry such guarantees, or "non-Agency RMBS," such as RMBS backed by prime jumbo, Alternative A-paper, manufactured housing, and subprime residential mortgage loans. Agency RMBS include both Agency pools and Agency collateralized mortgage obligations, or "CMOs," and non-Agency RMBS primarily consist of non-Agency CMOs, both investment grade and non-investment grade. The Company may also acquire and manage mortgage servicing rights, credit risk transfer securities, residential mortgage loans, and other mortgage- and real estate-related assets. The Company may also invest in other instruments including, but not limited to, forward-settling To-Be-Announced Agency pass-through certificates, or "TBAs," interest rate swaps and swaptions, U.S. Treasury securities, Eurodollar and U.S. Treasury futures, other financial derivatives, and cash equivalents. The Company's targeted investments may range from unrated first loss securities to AAA senior securities. The Company has elected to be taxed as a REIT under the Internal Revenue Code of 1986, as amended, or "the Code," and intends to conduct its operations to be qualified and taxed as a REIT. As a REIT, the Company is required to distribute annually at least 90% of its taxable income. As long as the Company continues to qualify as a REIT, it will not be subject to U.S. federal corporate taxes on its taxable income to the extent that it distributes all of its annual taxable income to its shareholders. It is the intention of the Company to distribute at least 100% of its taxable income, after application of available tax attributes, within the time limits prescribed by the Code, which may extend into the subsequent taxable year.

Organization and Investment Objective

Ellington Residential Mortgage REIT, or "EARN," was formed as a Maryland real estate investment trust, or "REIT," on August 2, 2012, and commenced operations on September 25, 2012. EARN conducts its business through its wholly owned subsidiaries, EARN OP GP LLC, or the "General Partner," and Ellington Residential Mortgage LP, or the "Operating Partnership," which were formed as a Delaware limited liability company and a Delaware limited partnership, respectively, on July 31, 2012 and commenced operations on September 25, 2012. The Operating Partnership conducts its business of acquiring, investing in, and managing residential mortgage- and real estate-related assets through its wholly owned subsidiaries. EARN, the General Partner, the Operating Partnership, and their consolidated subsidiaries are hereafter defined as the "Company."

Ellington Residential Mortgage Management LLC, or the "Manager," serves as the Manager of the Company pursuant to the terms of the Fifth Amended and Restated Management Agreement, or the "Management Agreement." The Manager is an affiliate of Ellington Management Group, L.L.C., or "EMG," an investment management firm that is an SEC-registered investment adviser with a 24-year history of investing in a broad spectrum of mortgage-backed securities and related derivatives, with an emphasis on the residential mortgage-backed securities, or "RMBS," market. In accordance with the terms of the Management Agreement and the Services Agreement (as described in Note 9), the Manager is responsible for administering the Company's business activities and day-to-day operations, and performs certain services, subject to oversight by the Board of Trustees. See Note 9 for further information on the Management Agreement.

The Company acquires and manages RMBS, for which the principal and interest payments are guaranteed by a U.S. government agency or a U.S. government-sponsored entity, or "Agency RMBS," and RMBS that do not carry such guarantees, or "non-Agency RMBS," such as RMBS backed by prime jumbo, Alternative A-paper, manufactured housing, and subprime residential mortgage loans. Agency RMBS include both Agency pools and Agency collateralized mortgage obligations, or "CMOs," and non-Agency RMBS primarily consist of non-Agency CMOs, both investment grade and non-investment grade. The Company may also acquire and manage mortgage servicing rights, credit risk transfer securities, residential mortgage loans, and other mortgage- and real estate-related assets. The Company may also invest in other instruments including, but not limited to, forward-settling To-Be-Announced Agency pass-through certificates, or "TBAs," interest rate swaps and swaptions, U.S. Treasury securities, Eurodollar and U.S. Treasury futures, other financial derivatives, and cash equivalents. The Company's targeted investments may range from unrated first loss securities to AAA senior securities.

The Company has elected to be taxed as a REIT under the Internal Revenue Code of 1986, as amended, or "the Code," and intends to conduct its operations to be qualified and taxed as a REIT. As a REIT, the Company is required to distribute annually at least 90% of its taxable income. As long as the Company continues to qualify as a REIT, it will not be subject to U.S. federal corporate taxes on its taxable income to the extent that it distributes all of its annual taxable income to its shareholders. It is the intention of the Company to distribute at least 100% of its taxable income, after application of available tax attributes, within the time limits prescribed by the Code, which may extend into the subsequent taxable year.