Organization	12 Months Ended
Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	Organization Equity Commonwealth (the Company) is a real estate investment trust, or REIT, formed in 1986 under the laws of the State of Maryland. Our business is the ownership and operation of real estate, primarily office buildings, throughout the United States. On November 10, 2016, the Company converted to what is commonly referred to as an umbrella partnership real estate investment trust, or UPREIT, structure. In connection with this conversion, the Company contributed substantially all of its assets to EQC Operating Trust, a Maryland real estate investment trust (the Operating Trust), and the Operating Trust assumed substantially all of the Company’s liabilities pursuant to a contribution and assignment agreement between the Company and the Operating Trust. The Company now conducts and intends to continue to conduct substantially all of its activities through the Operating Trust. The Company beneficially owned, 99.97% of the outstanding shares of beneficial interest, designated as units, in the Operating Trust (OP Units) as of December 31, 2017, and the Company is the sole trustee of the Operating Trust. As the sole trustee, the Company generally has the exclusive power under the declaration of trust of the Operating Trust to manage and conduct the business of the Operating Trust, subject to certain limited approval and voting rights of other holders of OP Units. At December 31, 2017, our portfolio, excluding properties held for sale, included 16 properties (26 buildings), with a combined 8.7 million square feet. As of December 31, 2017, we had $2.6 billion of cash and cash equivalents and marketable securities. All numbers of properties, numbers of buildings and square feet are unaudited.

Organization

Equity Commonwealth (the Company) is a real estate investment trust, or REIT, formed in 1986 under the laws of the State of Maryland. Our business is the ownership and operation of real estate, primarily office buildings, throughout the United States.

On November 10, 2016, the Company converted to what is commonly referred to as an umbrella partnership real estate investment trust, or UPREIT, structure. In connection with this conversion, the Company contributed substantially all of its assets to EQC Operating Trust, a Maryland real estate investment trust (the Operating Trust), and the Operating Trust assumed substantially all of the Company’s liabilities pursuant to a contribution and assignment agreement between the Company and the Operating Trust.

The Company now conducts and intends to continue to conduct substantially all of its activities through the Operating Trust. The Company beneficially owned, 99.97% of the outstanding shares of beneficial interest, designated as units, in the Operating Trust (OP Units) as of December 31, 2017, and the Company is the sole trustee of the Operating Trust. As the sole trustee, the Company generally has the exclusive power under the declaration of trust of the Operating Trust to manage and conduct the business of the Operating Trust, subject to certain limited approval and voting rights of other holders of OP Units.

At December 31, 2017, our portfolio, excluding properties held for sale, included 16 properties (26 buildings), with a combined 8.7 million square feet. As of December 31, 2017, we had $2.6 billion of cash and cash equivalents and marketable securities. All numbers of properties, numbers of buildings and square feet are unaudited.