Organization (Details 2) (Corporate Office Properties, L.P.)	6 Months Ended
	Jun. 30, 2012 Trustee
Common Units
Forms of ownership in Operating Partnership and ownership percentage by the entity
Percentage ownership in operating partnership	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%
Series H Preferred Units
Forms of ownership in Operating Partnership and ownership percentage by the entity
Percentage ownership in operating partnership	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%
Series J Preferred Units
Forms of ownership in Operating Partnership and ownership percentage by the entity
Percentage ownership in operating partnership	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%
Series L Preferred Units
Forms of ownership in Operating Partnership and ownership percentage by the entity
Percentage ownership in operating partnership	100.00%