Annual report pursuant to Section 13 and 15(d)

Significant Accounting Policies (Narrative) (Details)

v2.4.0.6
Significant Accounting Policies (Narrative) (Details) (USD $)
 3 Months Ended 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Jan. 04, 2013
Jan. 05, 2012
Dec. 31, 2009
Capitalized development and construction salaries and other related costs     $ 3,800,000 $ 3,700,000 $ 3,400,000      
Rental property in-progress 107,600,000 37,100,000 107,600,000 37,100,000        
Maximum period after cessation of major construction activity that projects are considered complete     1 year          
Consolidated joint ventures, total real estate assets 198,300,000   198,300,000          
Consolidated joint ventures, mortgages 77,100,000   77,100,000          
Consolidated joint ventures, other liabilities 16,500,000   16,500,000          
Amortization of deferred financing costs     2,669,000 2,370,000 2,656,000      
Write off of unamortized deferred financing costs     593,000          
Deferred leasing costs     4,354,000 4,432,000 3,986,000      
Common stock, shares outstanding 87,536,292 87,799,479 87,536,292 87,799,479   87,537,250 87,800,047  
Common units outstanding 12,141,836 12,197,122 12,141,836 12,197,122 13,007,668 12,141,836 12,197,122 13,495,036
Common stock dividends and common unit distributions per share $ 0.45 $ 0.45            
Dividends paid per common share     $ 1.80 $ 1.80 $ 1.80      
Dividends paid, percent representing ordinary income     75.00% 77.00% 75.00%      
Dividends paid, percent representing return of capital to shareholders     25.00% 23.00% 25.00%      
Restricted stock expense     $ 3,642,000 $ 4,123,000 $ 4,121,000      
Fourth Quarter 2012 [Member]
                
Distributions payable, record date     Jan. 04, 2013          
Common stock dividends and common unit distributions payable, date     Jan. 11, 2013          
Fourth Quarter 2011 [Member]
                
Distributions payable, record date     Jan. 05, 2012          
Common stock dividends and common unit distributions payable, date     Jan. 13, 2012