Summary of Significant Accounting Policies - Narative (Details) (USD $)
3 Months Ended 6 Months Ended
Jun. 30, 2012
Property
Jun. 30, 2011
Property
Jun. 30, 2012
Property
Jun. 30, 2011
Property
Dec. 31, 2011
Accounting Policies [Line Items]          
Number of properties with impairment indicators (in properties)     7    
Real estate investment property, net, with impairment indicators $ 53,100,000   $ 53,100,000    
Number of properties with impairment indicators with no impairment 6   6    
Number of properties impaired 1 0 1 0  
Impairment of real estate assets 1,979,000 0 1,979,000 0  
Assets 3,354,738,000   3,354,738,000   3,430,322,000
Unconsolidated joint ventures
         
Accounting Policies [Line Items]          
Assets 58,600,000   58,600,000   59,300,000
Notes payable $ 33,800,000   $ 33,800,000   $ 34,100,000