Common Shares	3 Months Ended
Mar. 31, 2015
Stockholders' Equity Note [Abstract]
Stockholders' Equity Note Disclosure [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 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 $500 million unsecured line of credit, 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, 2015 or 2014. 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, 2015 through the date of this filing. 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, 2015, we had approximately 86.8 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, 2015

Stockholders' Equity Note [Abstract]

Stockholders' Equity Note Disclosure [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 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 $500 million unsecured line of credit, 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, 2015 or 2014. 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, 2015 through the date of this filing.

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, 2015, we had approximately 86.8 million common shares outstanding, net of treasury shares and shares held in our deferred compensation arrangements, and no preferred shares outstanding.