Annual report pursuant to Section 13 and 15(d)

Real Estate Joint Ventures (Details)

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Real Estate Joint Ventures (Details) (USD $)
 12 Months Ended
Dec. 31, 2011
building
venture
Dec. 31, 2010
Dec. 31, 2009
Investments in real estate joint ventures      
Investment Balance $ (6,071,000) $ (5,545,000)  
Unconsolidated real estate joint ventures
      
Investments in real estate joint ventures      
Number of unconsolidated real estate joint ventures the entity has an interest in 1    
Investment Balance (6,071,000) (5,545,000)  
Ownership (as a percent) 20.00%    
Number of buildings operated by the joint venture 16    
Difference between carrying amount of investment and share of the equity in the joint venture 5,200,000 5,200,000  
Maximum exposure to loss 0    
Fees recognized from joint ventures for property management, construction and leasing services     119,000,000
Condensed balance sheets for unconsolidated real estate joint venture      
Properties, net 59,792,000 61,521,000  
Other assets 3,529,000 4,174,000  
Total assets 63,321,000 65,695,000  
Liabilities (primarily debt) 67,710,000 67,454,000  
Owners' equity (4,389,000) (1,759,000)  
Total liabilities and owners' equity 63,321,000 65,695,000  
Condensed statements of operations for unconsolidated real estate joint venture      
Revenues 7,577,000 8,405,000 9,031,000
Property operating expenses (3,673,000) (3,600,000) (3,438,000)
Interest expense (3,913,000) (3,937,000) (3,981,000)
Depreciation and amortization expense (2,463,000) (3,154,000) (3,198,000)
Net loss (2,472,000) (2,286,000) (1,586,000)
M Square Associates, LLC
      
Investments in real estate joint ventures      
Number of buildings operated by the joint venture 2    
Investments in consolidated real estate joint ventures      
Ownership (as a percent) 50.00%    
Total Assets 59,941,000    
Pledged Assets 47,901,000    
Total Liabilities 44,265,000    
LW Redstone Company, LLC
      
Investments in consolidated real estate joint ventures      
Ownership (as a percent) 85.00%    
Total Assets 48,985,000    
Total Liabilities 9,014,000    
Arundel Preserve 5, LLC
      
Investments in real estate joint ventures      
Number of buildings operated by the joint venture 1    
Investments in consolidated real estate joint ventures      
Ownership (as a percent) 50.00%    
Total Assets 30,254,000    
Pledged Assets 29,353,000    
Total Liabilities 17,343,000    
COPT-FD Indian Head, LLC
      
Investments in consolidated real estate joint ventures      
Ownership (as a percent) 75.00%    
Total Assets 6,538,000    
Total Liabilities 2,000    
MOR Forbes 2 LLC
      
Investments in real estate joint ventures      
Number of buildings operated by the joint venture 1    
Investments in consolidated real estate joint ventures      
Ownership (as a percent) 50.00%    
Total Assets 3,884,000    
Total Liabilities 29,000    
Consolidated real estate joint ventures
      
Investments in consolidated real estate joint ventures      
Total Assets 149,602,000    
Pledged Assets 77,254,000    
Total Liabilities $ 70,653,000