Quarterly report pursuant to Section 13 or 15(d)

Commitments and Contingencies (Details)

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Commitments and Contingencies (Details) (USD $)
 1 Months Ended 9 Months Ended
Aug. 31, 2010
Sep. 30, 2011
Year
property
segment
Sep. 30, 2011
Nonrecourse loan guarantees of unconsolidated partnership
Sep. 30, 2011
Arundel Preserve 5, LLC, Date Acquired 7/2/2007
sqfeet
acre
Joint Ventures        
Maximum approximate amount required to be paid under the guarantees     $ 65,000,000  
Recovery percentage of amount paid under the guarantee when the entity continues to manage the properties (as a percent)     20.00%  
Recovery percentage of amount paid under the guarantee when the entity no longer manages the properties (as a percent)     80.00%  
Office space to be developed with a limited partnership (in square feet)       1,800,000
Land available to develop office space (in acres)       63
Ownership (as a percent)       50.00%
Tax incremental financing obligation        
The amount of tax incremental financing bonds issued by Anne Arundel County, Maryland 30,000,000      
Liability recognized with regard to tax incremental financing obligation at end of current period   4,300,000    
Environmental indemnity agreement        
Number of lease properties which were provided environmental indemnifications   3    
Environmental indemnification to the tenant against losses covered under prior owner's indemnity agreement   5,000,000    
Length of environmental indemnification to the tenant against consequential damages at a building after the tenant's acquisition of the property (in years)   15    
Maximum environmental indemnification to the tenant against consequential damages after acquisition of property   12,500,000    
Additional costs agreed to be paid by the entity related to construction and environmental regulatory activities (as a percent)   50.00%    
Maximum annual additional costs agreed to be paid by the entity related to construction and environmental regulatory activities   300,000    
Maximum additional costs agreed to be paid by the entity related to construction and environmental regulatory activities   $ 1,500,000