COPT Defense Properties Annual report pursuant to Section 13 and 15(d)

Properties, net (Details 4) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 sqfeet property
Dispositions
Number of Buildings	23
Total Rentable Square Feet	894,000
Sale Price	$ 76,660
Gain on Sale	4,807
1344 & 1348 Ashton Road and 1350 Dorsey Road
Dispositions
Number of Buildings	3
Total Rentable Square Feet	39,000
Sale Price	3,800
Gain on Sale	150
216 Schilling Circle
Dispositions
Number of Buildings	1
Total Rentable Square Feet	36,000
Sale Price	4,700
Gain on Sale	175
Towson Portfolio
Dispositions
Number of Buildings	4
Total Rentable Square Feet	179,000
Sale Price	16,000
Gain on Sale	1,134
11011 McCormick Road
Dispositions
Number of Buildings	1
Total Rentable Square Feet	57,000
Sale Price	3,450
Gain on Sale	822
10001 Franklin Square Drive
Dispositions
Number of Buildings	1
Total Rentable Square Feet	218,000
Sale Price	16,250
Gain on Sale	305
Rutherford Business Center Portfolio
Dispositions
Number of Buildings	13
Total Rentable Square Feet	365,000
Sale Price	32,460
Gain on Sale	$ 2,221