Unsecured Line of Credit	12 Months Ended
Dec. 31, 2013
Unsecured Line of Credit [Abstract]
Unsecured Line of Credit [Text Block]	9. Unsecured Line of Credit On July 26, 2013, the Company's Operating Partnership amended and restated the revolving credit agreement governing the Company's Unsecured Line of Credit, which, among other things, (1) increased the total commitment from $750.0 million to $1.0 billion, (2) extended the maturity date from June 24, 2014 to July 26, 2018 and (3) reduced the per annum variable interest rates and other fees. The Operating Partnership may increase the total commitment to $1.5 billion, subject to syndication of the increase and other conditions. At the Operating Partnership’s option, loans outstanding under the Unsecured Line of Credit will bear interest at a rate per annum equal to (1), in the case of loans denominated in Dollars, Euro or Sterling, LIBOR or, in the case of loans denominated in Canadian Dollars, CDOR, in each case, plus a margin ranging from 0.925% to 1.70% based on the Operating Partnership’s credit rating or (2) an alternate base rate equal to the greatest of (a) the Administrative Agent’s prime rate, (b) the Federal Funds rate plus 0.5% or (c) LIBOR for a one month period plus 1.00%, in each case, plus a margin ranging from 0.0% to 0.70% based on the Operating Partnership’s credit rating. The Unsecured Line of Credit also contains a competitive bid option that allows banks that are part of the lender consortium to bid to make loan advances to the Operating Partnership at a reduced interest rate. In addition, the Operating Partnership is also obligated to pay (1) in quarterly installments a facility fee on the total commitment at a rate per annum ranging from 0.125% to 0.35% based on the Operating Partnership’s credit rating and (2) an annual fee on the undrawn amount of each letter of credit equal to the LIBOR margin. Based on the Operating Partnership’s current credit rating, the LIBOR and CDOR margin is 1.00%, the alternate base rate margin is 0.0% and the facility fee is 0.15%. At December 31, 2013 and 2012, there were no amounts outstanding on the Unsecured Line of Credit. The terms of the Unsecured Line of Credit require that the Company maintain a number of customary financial and other covenants on an ongoing basis, including: (1) a leverage ratio not to exceed 60%, however, the leverage ratio may increase to no greater than 65% provided that it is reduced back to 60% within one year, (2) a secured debt leverage ratio not to exceed 55%, (3) a fixed charge coverage ratio of at least 1.40, (4) an unsecured debt leverage ratio not to exceed 60%, however, the unsecured debt leverage ratio may increase to no greater than 65% provided that it is reduced back to 60% within one year, (5) an unsecured debt interest coverage ratio of at least 1.75 and (6) limitations on permitted investments. At December 31, 2013, the Company was in compliance with each of these financial and other covenant requirements.

9. Unsecured Line of Credit

On July 26, 2013, the Company's Operating Partnership amended and restated the revolving credit agreement governing the Company's Unsecured Line of Credit, which, among other things, (1) increased the total commitment from $750.0 million to $1.0 billion, (2) extended the maturity date from June 24, 2014 to July 26, 2018 and (3) reduced the per annum variable interest rates and other fees. The Operating Partnership may increase the total commitment to $1.5 billion, subject to syndication of the increase and other conditions. At the Operating Partnership’s option, loans outstanding under the Unsecured Line of Credit will bear interest at a rate per annum equal to (1), in the case of loans denominated in Dollars, Euro or Sterling, LIBOR or, in the case of loans denominated in Canadian Dollars, CDOR, in each case, plus a margin ranging from 0.925% to 1.70% based on the Operating Partnership’s credit rating or (2) an alternate base rate equal to the greatest of (a) the Administrative Agent’s prime rate, (b) the Federal Funds rate plus 0.5% or (c) LIBOR for a one month period plus 1.00%, in each case, plus a margin ranging from 0.0% to 0.70% based on the Operating Partnership’s credit rating. The Unsecured Line of Credit also contains a competitive bid option that allows banks that are part of the lender consortium to bid to make loan advances to the Operating Partnership at a reduced interest rate. In addition, the Operating Partnership is also obligated to pay (1) in quarterly installments a facility fee on the total commitment at a rate per annum ranging from 0.125% to 0.35% based on the Operating Partnership’s credit rating and (2) an annual fee on the undrawn amount of each letter of credit equal to the LIBOR margin. Based on the Operating Partnership’s current credit rating, the LIBOR and CDOR margin is 1.00%, the alternate base rate margin is 0.0% and the facility fee is 0.15%. At December 31, 2013 and 2012, there were no amounts outstanding on the Unsecured Line of Credit.

The terms of the Unsecured Line of Credit require that the Company maintain a number of customary financial and other covenants on an ongoing basis, including: (1) a leverage ratio not to exceed 60%, however, the leverage ratio may increase to no greater than 65% provided that it is reduced back to 60% within one year, (2) a secured debt leverage ratio not to exceed 55%, (3) a fixed charge coverage ratio of at least 1.40, (4) an unsecured debt leverage ratio not to exceed 60%, however, the unsecured debt leverage ratio may increase to no greater than 65% provided that it is reduced back to 60% within one year, (5) an unsecured debt interest coverage ratio of at least 1.75 and (6) limitations on permitted investments. At December 31, 2013, the Company was in compliance with each of these financial and other covenant requirements.