Significant Accounting Policies (Narrative) (Details) (USD $)
3 Months Ended9 Months Ended12 Months Ended
Sep. 30, 2011
Dec. 31, 2010
Sep. 30, 2010
Sep. 30, 2011
Sep. 30, 2010
Dec. 31, 2010
Oct. 05, 2011
Jan. 05, 2011
Significant Accounting Policies [Abstract]        
Rental property in progress$ 30,948,000$ 65,990,000 $ 30,948,000 $ 65,990,000  
Amortization of deferred financing costs584,000 646,0001,752,0002,021,000   
Deferred leasing costs1,099,000 872,0003,135,0002,728,000   
Minimum percentage of REIT taxable income distributed to shareholders   90.00%    
Preferred stock, shares outstanding10,00010,000 10,000 10,00010,00010,000
Common stock, shares outstanding87,141,71679,605,474 87,141,716 79,605,47487,142,00479,605,542
Common units outstanding12,771,10513,007,668 12,771,105 13,007,66812,771,10513,007,668
Preferred stock dividends per share     $ 50.00  
Preferred stock dividends per share declared$ 50.00       
Common unit distributions per share$ 0.45$ 0.45      
Restricted stock expense$ 690,000 $ 626,000$ 2,070,000$ 1,869,000