Note 1 - Organization and Formation of the Company	9 Months Ended
Sep. 30, 2012
Nature of Operations [Text Block]	1. Organization and Formation of the Company Mission West Properties, Inc. (the “Company”) is a fully integrated, self-administered and self-managed real estate company that acquires and manages research and development (“R&D”)/office properties in the portion of the San Francisco Bay Area commonly referred to as Silicon Valley. In July 1998, the Company purchased an approximate 12.11% interest in four existing limited partnerships (referred to collectively as the “operating partnerships”) and obtained control of these partnerships by becoming the sole general partner in each one effective July 1, 1998, for financial accounting and reporting purposes. All limited partnership interests in the operating partnerships were converted into 59,479,633 operating partnership (“O.P.”) units, which represented a limited partnership ownership interest of approximately 87.89% of the operating partnerships. The operating partnerships are the vehicles through which the Company holds its real estate investments, makes real estate acquisitions, and generally conducts its business. On December 30, 1998, the Company was reincorporated under the laws of the State of Maryland through a merger with and into Mission West Properties, Inc. Accordingly, shares of the former company, Mission West Properties, a California corporation (no par), which were outstanding at December 30, 1998, were converted into shares of common stock, $.001 par value per share, on a one-for-one basis. In late December 2011, the Company formed two additional operating partnerships and transferred certain R&D properties from two current operating partnerships into the two new operating partnerships through two separate partnership division transactions. The two transactions changed the nominal ownership of title to certain properties but did not modify the economic interests or rights of the Company or the limited partners in the operating partnerships. The Company is the sole general partner of the two new operating partnerships. There was no issuance of common shares associated with these transactions, and the number of O.P. units issued in each of the new operating partnerships was fully offset by the cancellation of the same number O.P. units of each respective predecessor operating partnership. As of September 30, 2012, the Company owned a controlling general partnership interest of 25.89%, 21.86%, 16.32%, 12.53%, 21.86% and 16.32% in Mission West Properties, L.P., Mission West Properties, L.P. I, Mission West Properties, L.P. II, Mission West Properties, L.P. III, Mission West Properties, L.P. IV and Mission West Properties, L.P. V, respectively, which represents a 21.52% general partnership interest in the operating partnerships, taken as a whole, on a consolidated weighted average basis. The ownership interests which the Company does not own in the operating partnerships are accounted for as noncontrolling interests. Through the operating partnerships, the Company owns interests in 101 R&D/office properties, all of which are located in the Silicon Valley. The Company has elected to be taxed as a Real Estate Investment Trust (“REIT”) under the Internal Revenue Code of 1986, as amended. Accordingly, no provision has been made for income taxes for the three and nine months ended September 30, 2012 and 2011. Business Segment Information The Company’s primary business is the ownership and management of R&D/office real estate with a geographic concentration in the Silicon Valley of the San Francisco Bay Area. Accordingly, the Company has concluded it currently has a single reportable segment for the Segment Reporting Topic of the Financial Accounting Standards Board Accounting Standards Codification (“FASB ASC”) 280 purposes.

Note 1 - Organization and Formation of the Company

9 Months Ended

Sep. 30, 2012

1. Organization and Formation of the Company

Mission West Properties, Inc. (the “Company”) is a fully integrated, self-administered and self-managed real estate company that acquires and manages research and development (“R&D”)/office properties in the portion of the San Francisco Bay Area commonly referred to as Silicon Valley. In July 1998, the Company purchased an approximate 12.11% interest in four existing limited partnerships (referred to collectively as the “operating partnerships”) and obtained control of these partnerships by becoming the sole general partner in each one effective July 1, 1998, for financial accounting and reporting purposes. All limited partnership interests in the operating partnerships were converted into 59,479,633 operating partnership (“O.P.”) units, which represented a limited partnership ownership interest of approximately 87.89% of the operating partnerships. The operating partnerships are the vehicles through which the Company holds its real estate investments, makes real estate acquisitions, and generally conducts its business.

On December 30, 1998, the Company was reincorporated under the laws of the State of Maryland through a merger with and into Mission West Properties, Inc. Accordingly, shares of the former company, Mission West Properties, a California corporation (no par), which were outstanding at December 30, 1998, were converted into shares of common stock, $.001 par value per share, on a one-for-one basis.

In late December 2011, the Company formed two additional operating partnerships and transferred certain R&D properties from two current operating partnerships into the two new operating partnerships through two separate partnership division transactions. The two transactions changed the nominal ownership of title to certain properties but did not modify the economic interests or rights of the Company or the limited partners in the operating partnerships. The Company is the sole general partner of the two new operating partnerships. There was no issuance of common shares associated with these transactions, and the number of O.P. units issued in each of the new operating partnerships was fully offset by the cancellation of the same number O.P. units of each respective predecessor operating partnership.

As of September 30, 2012, the Company owned a controlling general partnership interest of 25.89%, 21.86%, 16.32%, 12.53%, 21.86% and 16.32% in Mission West Properties, L.P., Mission West Properties, L.P. I, Mission West Properties, L.P. II, Mission West Properties, L.P. III, Mission West Properties, L.P. IV and Mission West Properties, L.P. V, respectively, which represents a 21.52% general partnership interest in the operating partnerships, taken as a whole, on a consolidated weighted average basis. The ownership interests which the Company does not own in the operating partnerships are accounted for as noncontrolling interests. Through the operating partnerships, the Company owns interests in 101 R&D/office properties, all of which are located in the Silicon Valley.

The Company has elected to be taxed as a Real Estate Investment Trust (“REIT”) under the Internal Revenue Code of 1986, as amended. Accordingly, no provision has been made for income taxes for the three and nine months ended September 30, 2012 and 2011.

Business Segment Information

The Company’s primary business is the ownership and management of R&D/office real estate with a geographic concentration in the Silicon Valley of the San Francisco Bay Area. Accordingly, the Company has concluded it currently has a single reportable segment for the Segment Reporting Topic of the Financial Accounting Standards Board Accounting Standards Codification (“FASB ASC”) 280 purposes.