Organization (Details 2) (Corporate Office Properties, L.P.)	12 Months Ended
	Dec. 31, 2011 trustee	Dec. 31, 2010
Common Units
Forms of ownership in Operating Partnership and ownership percentage by the entity
Percentage ownership in operating partnership	94.00%	94.00%
Number of trustees controlling additional common units	3
Additional percentage of common units controlled by trustees (as a percent)	5.00%
Series G Preferred Units
Forms of ownership in Operating Partnership and ownership percentage by the entity
Percentage ownership in operating partnership	100.00%	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%