Subsequent Events	3 Months Ended
Subsequent Events	Mar. 31, 2012
Subsequent Events [Abstract]
Subsequent Events	13. Subsequent Events From April 1, 2012 through May 8, 2012, the Company issued an aggregate of 643,600 shares of its Common Stock under the ATM program for gross proceeds of approximately $68.4 million and net proceeds of approximately $67.7 million. As of May 8, 2012, approximately $376.2 million remained available for issuance under this ATM program. On April 2, 2012, the Company used available cash to repay the mortgage loan collateralized by its One Freedom Square property located in Reston, Virginia totaling $65.1 million. The mortgage financing bore interest at a fixed rate of 7.75% per annum and was scheduled to mature on June 30, 2012. There was no prepayment penalty. On April 30, 2012, the Company completed and placed in-service 510 Madison Avenue, a Class A office project with approximately 347,000 net rentable square feet located in New York City. On May 1, 2012, the Company entered into an agreement to sell its Bedford Business Park properties located in Bedford, Massachusetts for approximately $62.8 million in cash. Bedford Business Park is comprised of two Office/Technical buildings and one Class A office building aggregating approximately 470,000 net rentable square feet. The sale is subject to the satisfaction of customary closing conditions and there can be no assurance that the sale will be consummated on the terms currently contemplated or at all. On May 3, 2012, the Company completed and placed in-service 12310 Sunrise Valley Drive, a Class A office redevelopment project with approximately 268,000 net rentable square feet located in Reston, Virginia.

Tabular disclosure of significant events or transactions that occurred after the balance sheet date through the date the financial statements were issued or the date the financial statements were available to be issued. Examples include: the sale of a capital stock issue, purchase of a business, settlement of litigation, losses resulting from fire or flood, losses on receivables, significant realized and unrealized gains and losses that result from changes in quoted market prices of securities, declines in market prices of inventory, changes in authorized or issued debt (SEC), significant foreign exchange rate changes, substantial loans to insiders or affiliates, significant long-term investments, and substantial dividends not in the ordinary course of business.

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