Annual report pursuant to Section 13 and 15(d)

Organization (Details 2)

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Organization (Details 2) (Corporate Office Properties, L.P.)
12 Months Ended
Dec. 31, 2012
Trustee
Dec. 31, 2011
Common Units
   
Forms of ownership in Operating Partnership and ownership percentage by the entity    
Percentage ownership in operating partnership 95.00% 94.00%
Number of trustees controlling additional common units 3  
Additional percentage of common units controlled by trustees (as a percent) 4.00%  
Series G Preferred Units
   
Forms of ownership in Operating Partnership and ownership percentage by the entity    
Percentage ownership in operating partnership   100.00%
Series H Preferred Units
   
Forms of ownership in Operating Partnership and ownership percentage by the entity    
Percentage ownership in operating partnership 100.00% 100.00%
Series I Preferred Units
   
Forms of ownership in Operating Partnership and ownership percentage by the entity    
Percentage ownership in operating partnership 0.00% 0.00%
Series J Preferred Units
   
Forms of ownership in Operating Partnership and ownership percentage by the entity    
Percentage ownership in operating partnership 100.00% 100.00%
Series K Preferred Units
   
Forms of ownership in Operating Partnership and ownership percentage by the entity    
Percentage ownership in operating partnership 100.00% 100.00%
Series L Preferred Units
   
Forms of ownership in Operating Partnership and ownership percentage by the entity    
Percentage ownership in operating partnership 100.00%