Earnings Per Share ("EPS") and Earnings Per Unit (“EPU”) (Details 2) - shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Conversion of common units [Member]
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares)	0	3,897,000	3,869,000
Conversion of Series I preferred units [Member]
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares)	176,000	176,000	176,000
Conversion of Series K preferred shares [Member]
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares)	434,000	434,000	434,000
Stock Options [Member]
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares)	469,000	492,000	636,000
Restricted Stock and Deferred Shares [Member]
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares)	410,000	401,000	385,000
Corporate Office Properties, L.P. [Member] | Stock Options [Member]
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares)	469,000	492,000	636,000
Corporate Office Properties, L.P. [Member] | Restricted Stock and Deferred Shares [Member]
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares)	410,000	401,000	385,000
Corporate Office Properties, L.P. [Member] | Conversion of Series I preferred units [Member]
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares)	176,000	176,000	176,000
Corporate Office Properties, L.P. [Member] | Conversion of Series K preferred units [Member]
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares)	434,000	434,000	434,000