Common Shares	3 Months Ended
Mar. 31, 2016
Stockholders' Equity Note [Abstract]
Common Shares [Text Block]	4. Common Shares In November 2014, we created an at-the-market ("ATM") share offering program through which we can, but have no obligation to, sell common shares having an aggregate offering price of up to $331.3 million (the "2014 ATM program"), in amounts and at times as we determine, into the existing trading market at current market prices as well as through privately negotiated transactions. Actual sales from time to time may depend on a variety of factors including, among others, market conditions, the trading price of our common shares, and determinations by management of the appropriate sources of funding for us. We intend to use the net proceeds from any future sales under the 2014 ATM program for general corporate purposes, which may include reducing future borrowings under our unsecured credit facility or other short-term borrowings, the repayment of other indebtedness, the redemption or other repurchase of outstanding debt or equity securities, funding for development, redevelopment and investment projects and financing for acquisitions. There were no shares sold during the three months ended March 31, 2016 or 2015 under the 2014 ATM program. As of the date of this filing, we had common shares having an aggregate offering price of up to $315.3 million remaining available for sale under the 2014 ATM program. No shares were sold subsequent to March 31, 2016 through the date of this filing under the 2014 ATM program. In January 2008, our Board of Trust Managers approved an increase of the April 2007 repurchase plan to allow for the repurchase of up to $500 million of our common equity securities through open market purchases, block purchases, and privately negotiated transactions. Under this program, we repurchased 4.3 million shares for a total of approximately $230.2 million from April 2007 through December 31, 2008 and there have not been any shares repurchased subsequent to that date. As of the date of this filing, the remaining dollar value of our common equity securities authorized to be repurchased under the program was approximately $269.8 million. We currently have an automatic shelf registration statement which allows us to offer, from time to time, common shares, preferred shares, debt securities, or warrants. Our Amended and Restated Declaration of Trust provides we may issue up to 185 million shares of beneficial interest, consisting of 175 million common shares and 10 million preferred shares. At March 31, 2016, we had approximately 87.0 million common shares outstanding, net of treasury shares and shares held in our deferred compensation arrangements, and no preferred shares outstanding.

Common Shares

3 Months Ended

Mar. 31, 2016

Stockholders' Equity Note [Abstract]

4. Common Shares

In November 2014, we created an at-the-market ("ATM") share offering program through which we can, but have no obligation to, sell common shares having an aggregate offering price of up to $331.3 million (the "2014 ATM program"), in amounts and at times as we determine, into the existing trading market at current market prices as well as through privately negotiated transactions. Actual sales from time to time may depend on a variety of factors including, among others, market conditions, the trading price of our common shares, and determinations by management of the appropriate sources of funding for us. We intend to use the net proceeds from any future sales under the 2014 ATM program for general corporate purposes, which may include reducing future borrowings under our unsecured credit facility or other short-term borrowings, the repayment of other indebtedness, the redemption or other repurchase of outstanding debt or equity securities, funding for development, redevelopment and investment projects and financing for acquisitions.

There were no shares sold during the three months ended March 31, 2016 or 2015 under the 2014 ATM program. As of the date of this filing, we had common shares having an aggregate offering price of up to $315.3 million remaining available for sale under the 2014 ATM program. No shares were sold subsequent to March 31, 2016 through the date of this filing under the 2014 ATM program.

In January 2008, our Board of Trust Managers approved an increase of the April 2007 repurchase plan to allow for the repurchase of up to $500 million of our common equity securities through open market purchases, block purchases, and privately negotiated transactions. Under this program, we repurchased 4.3 million shares for a total of approximately $230.2 million from April 2007 through December 31, 2008 and there have not been any shares repurchased subsequent to that date. As of the date of this filing, the remaining dollar value of our common equity securities authorized to be repurchased under the program was approximately $269.8 million.

We currently have an automatic shelf registration statement which allows us to offer, from time to time, common shares, preferred shares, debt securities, or warrants. Our Amended and Restated Declaration of Trust provides we may issue up to 185 million shares of beneficial interest, consisting of 175 million common shares and 10 million preferred shares. At March 31, 2016, we had approximately 87.0 million common shares outstanding, net of treasury shares and shares held in our deferred compensation arrangements, and no preferred shares outstanding.