Earnings Per Share ("EPS") and Earnings Per Unit ("EPU") (Details 2) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Conversion of common units
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	3,221	3,446
Conversion of Series I preferred units
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	176	176
Forward Equity Sale Agreement
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	7,500
Weighted average restricted stock and deferred shares
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	444	392
Weighted average options
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	60	140
Corporate Office Properties, L.P. | Forward Equity Sale Agreement
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	7,500
Corporate Office Properties, L.P. | Weighted average restricted stock and deferred shares
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	444	392
Corporate Office Properties, L.P. | Weighted average options
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	60	140
Corporate Office Properties, L.P. | Conversion of Series I preferred units
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	176	176