Common Shares	3 Months Ended
Mar. 31, 2019
Stockholders' Equity Note [Abstract]
Common Shares [Text Block]	6. Common Shares In May 2017, 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 $315.3 million (the "2017 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. The proceeds from the sale of our common shares under the 2017 ATM program are intended to be used for general corporate purposes, which may include reducing future borrowings under our $900 million unsecured line of credit, the repayment of other indebtedness, the redemption or other repurchase of outstanding debt or equity securities, funding for development activities, and financing for acquisitions. For the three months ended March 31, 2019, and through the date of this filing, we did not sell any shares under the 2017 ATM program. As of the date of this filing, we had common shares having an aggregate offering price of up to $312.8 million remaining available for sale under the 2017 ATM program. We have a repurchase plan approved by our Board of Trust Managers which allows for the repurchase of up to $500 million of our common equity securities through open-market purchases, block purchases, and privately negotiated transactions. There were no repurchases during the three months ended March 31, 2019. As of the date of this filing, the remaining dollar value of our common equity securities authorized to be repurchased under this program was approximately $269.5 million. We currently have an automatic shelf registration statement which allows us to offer common shares, preferred shares, debt securities, or warrants, and 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, 2019, we had approximately 96.7 million common shares outstanding, net of treasury shares and shares held in our deferred compensation arrangements, and no preferred shares outstanding. In February 2019, we issued approximately 3.4 million common shares in an underwritten equity offering and received approximately $328.4 million in net proceeds, which we used to acquire one operating property in Scottsdale, Arizona, and repay amounts on our unsecured line of credit and certain secured conventional mortgage debt.

6. Common Shares

In May 2017, 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 $315.3 million (the "2017 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. The proceeds from the sale of our common shares under the 2017 ATM program are intended to be used for general corporate purposes, which may include reducing future borrowings under our $900 million unsecured line of credit, the repayment of other indebtedness, the redemption or other repurchase of outstanding debt or equity securities, funding for development activities, and financing for acquisitions.

For the three months ended March 31, 2019, and through the date of this filing, we did not sell any shares under the 2017 ATM program. As of the date of this filing, we had common shares having an aggregate offering price of up to $312.8 million remaining available for sale under the 2017 ATM program.

We have a repurchase plan approved by our Board of Trust Managers which allows for the repurchase of up to $500 million of our common equity securities through open-market purchases, block purchases, and privately negotiated transactions. There were no repurchases during the three months ended March 31, 2019. As of the date of this filing, the remaining dollar value of our common equity securities authorized to be repurchased under this program was approximately $269.5 million.

We currently have an automatic shelf registration statement which allows us to offer common shares, preferred shares, debt securities, or warrants, and 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, 2019, we had approximately 96.7 million common shares outstanding, net of treasury shares and shares held in our deferred compensation arrangements, and no preferred shares outstanding. In February 2019, we issued approximately 3.4 million common shares in an underwritten equity offering and received approximately $328.4 million in net proceeds, which we used to acquire one operating property in Scottsdale, Arizona, and repay amounts on our unsecured line of credit and certain secured conventional mortgage debt.