Organization	12 Months Ended
Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	Organization Western Asset Mortgage Capital Corporation, is a Delaware corporation, and its subsidiary (the "Company") commenced operations in May 2012. The Company invests in, finances and manages a diversified portfolio of real estate related securities, whole-loans and other financial assets. The Company's portfolio is comprised of Agency CMBS, Agency RMBS (including TBAs), Non-Agency RMBS, Non-Agency CMBS and Whole-Loans. In addition, and to a significantly lesser extent, the Company has invested in other securities including certain Agency obligations that are not technically MBS as well as certain Non U.S. CMBS and in asset-backed securities ("ABS") investments secured by a portfolio of private student loans. The Company's investment strategy is based on Western Asset Management Company's (the "Manager") perspective of which mix of portfolio assets it believes provides the Company with the best risk-reward opportunities at any given time. The Manager will vary the allocation among various asset classes subject to maintaining the Company's qualification as a REIT and maintaining its exemption from the Investment Company Act of 1940 (the "1940 Act"). These restrictions limit the Company's ability to invest in non-qualifying MBS, non-real estate assets and/or assets which are not secured by real estate. Accordingly, the Company's portfolio will continue to be principally invested in qualifying MBS, Whole-Loans and other real estate related assets. The Company is externally managed by the Manager, an investment advisor registered with the Securities and Exchange Commission ("SEC"). The Manager is a wholly-owned subsidiary of Legg Mason, Inc. The Company operates and has elected to be taxed as a real estate investment trust or "REIT" commencing with its taxable year ended December 31, 2012.

Organization

Western Asset Mortgage Capital Corporation, is a Delaware corporation, and its subsidiary (the "Company") commenced operations in May 2012. The Company invests in, finances and manages a diversified portfolio of real estate related securities, whole-loans and other financial assets. The Company's portfolio is comprised of Agency CMBS, Agency RMBS (including TBAs), Non-Agency RMBS, Non-Agency CMBS and Whole-Loans. In addition, and to a significantly lesser extent, the Company has invested in other securities including certain Agency obligations that are not technically MBS as well as certain Non U.S. CMBS and in asset-backed securities ("ABS") investments secured by a portfolio of private student loans. The Company's investment strategy is based on Western Asset Management Company's (the "Manager") perspective of which mix of portfolio assets it believes provides the Company with the best risk-reward opportunities at any given time. The Manager will vary the allocation among various asset classes subject to maintaining the Company's qualification as a REIT and maintaining its exemption from the Investment Company Act of 1940 (the "1940 Act"). These restrictions limit the Company's ability to invest in non-qualifying MBS, non-real estate assets and/or assets which are not secured by real estate. Accordingly, the Company's portfolio will continue to be principally invested in qualifying MBS, Whole-Loans and other real estate related assets.

The Company is externally managed by the Manager, an investment advisor registered with the Securities and Exchange Commission ("SEC"). The Manager is a wholly-owned subsidiary of Legg Mason, Inc. The Company operates and has elected to be taxed as a real estate investment trust or "REIT" commencing with its taxable year ended December 31, 2012.