Organization	12 Months Ended
Dec. 31, 2011
Organization [Abstract]
Organization	1. ORGANIZATION CYS Investments, Inc. (the "Company") (formerly known as Cypress Sharpridge Investments, Inc.) was formed as a Maryland corporation on January 3, 2006, and commenced operations on February 10, 2006. The Company has elected to be taxed and intends to continue to qualify as a real estate investment trust ("REIT") and is required to comply with the provisions of the Internal Revenue Code of 1986, as amended (the "Code"), with respect thereto. The Company's strategy had been to invest a majority of its capital in residential mortgage-backed securities that are issued and the principal and interest of which are guaranteed by a federally chartered corporation ("Agency RMBS"), such as the Federal National Mortgage Association ("Fannie Mae") or the Federal Home Loan Mortgage Corporation ("Freddie Mac"), or an agency of the U.S. government such as the Government National Mortgage Association ("Ginnie Mae"), and subordinated tranches of asset-backed securities, including collateralized debt or loan obligations ("CLOs"). Beginning in March 2008, pursuant to the Company's investment guidelines, the Company must invest exclusively in Agency RMBS, including collateralized mortgage obligations issued by Fannie Mae, Freddie Mac or Ginnie Mae. The Company's common stock trades on the New York Stock Exchange under the symbol "CYS." On September 1, 2011, the Company acquired certain assets and entered into agreements to internalize the Company's management (the "Internalization"). Prior to the Internalization, the Company had been managed by Cypress Sharpridge Advisors LLC (the "Manager") pursuant to a management agreement (the "Management Agreement"). The Manager had entered into sub-advisory agreements with Sharpridge Capital Management, L.P. ("Sharpridge") and an affiliate of The Cypress Group, pursuant to which the Manager was provided with all of the resources and assets (the "Assets") used to operate the Company's business and manage the Company's assets. In connection with the completion of the Internalization, the Management Agreement, sub-advisory agreements and other ancillary agreements related thereto were terminated. No termination fee was incurred or paid as a result of terminating those agreements. Under the terms of the Asset Purchase and Sale Agreement entered into in connection with the Internalization, the Company acquired the Assets and assumed the liabilities from Sharpridge for a purchase price of $750,000 of cash consideration. Additionally, all employees of Sharpridge as of August 31, 2011 were hired by the Company. In connection with the execution of his employment agreement, the Company's Chief Executive Officer received 150,000 shares of restricted stock on September 1, 2011 that vest ratably over a five year vesting period, with one-fifth of the shares vesting on each of the first five anniversary dates of the grant date. In addition, the Company accelerated the vesting of the Chief Executive Officer's outstanding shares of restricted stock issued prior to September 1, 2011, so that all such shares were vested and non-forfeitable on August 31, 2011, immediately prior to the completion of the Internalization. In connection with the Internalization, the Company changed its name from "Cypress Sharpridge Investments, Inc." to "CYS Investments, Inc." on September 1, 2011. The results of the Internalization were not material to the Company's results of operations.

Organization

12 Months Ended

Dec. 31, 2011

1. ORGANIZATION

CYS Investments, Inc. (the "Company") (formerly known as Cypress Sharpridge Investments, Inc.) was formed as a Maryland corporation on January 3, 2006, and commenced operations on February 10, 2006. The Company has elected to be taxed and intends to continue to qualify as a real estate investment trust ("REIT") and is required to comply with the provisions of the Internal Revenue Code of 1986, as amended (the "Code"), with respect thereto. The Company's strategy had been to invest a majority of its capital in residential mortgage-backed securities that are issued and the principal and interest of which are guaranteed by a federally chartered corporation ("Agency RMBS"), such as the Federal National Mortgage Association ("Fannie Mae") or the Federal Home Loan Mortgage Corporation ("Freddie Mac"), or an agency of the U.S. government such as the Government National Mortgage Association ("Ginnie Mae"), and subordinated tranches of asset-backed securities, including collateralized debt or loan obligations ("CLOs"). Beginning in March 2008, pursuant to the Company's investment guidelines, the Company must invest exclusively in Agency RMBS, including collateralized mortgage obligations issued by Fannie Mae, Freddie Mac or Ginnie Mae. The Company's common stock trades on the New York Stock Exchange under the symbol "CYS."

On September 1, 2011, the Company acquired certain assets and entered into agreements to internalize the Company's management (the "Internalization"). Prior to the Internalization, the Company had been managed by Cypress Sharpridge Advisors LLC (the "Manager") pursuant to a management agreement (the "Management Agreement"). The Manager had entered into sub-advisory agreements with Sharpridge Capital Management, L.P. ("Sharpridge") and an affiliate of The Cypress Group, pursuant to which the Manager was provided with all of the resources and assets (the "Assets") used to operate the Company's business and manage the Company's assets. In connection with the completion of the Internalization, the Management Agreement, sub-advisory agreements and other ancillary agreements related thereto were terminated. No termination fee was incurred or paid as a result of terminating those agreements.

Under the terms of the Asset Purchase and Sale Agreement entered into in connection with the Internalization, the Company acquired the Assets and assumed the liabilities from Sharpridge for a purchase price of $750,000 of cash consideration. Additionally, all employees of Sharpridge as of August 31, 2011 were hired by the Company. In connection with the execution of his employment agreement, the Company's Chief Executive Officer received 150,000 shares of restricted stock on September 1, 2011 that vest ratably over a five year vesting period, with one-fifth of the shares vesting on each of the first five anniversary dates of the grant date. In addition, the Company accelerated the vesting of the Chief Executive Officer's outstanding shares of restricted stock issued prior to September 1, 2011, so that all such shares were vested and non-forfeitable on August 31, 2011, immediately prior to the completion of the Internalization. In connection with the Internalization, the Company changed its name from "Cypress Sharpridge Investments, Inc." to "CYS Investments, Inc." on September 1, 2011. The results of the Internalization were not material to the Company's results of operations.