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Earnings Per Share ("EPS") and Earnings Per Unit (“EPU”) (Details 2) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Conversion of common units [Member]
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares)	3,633,000	0	3,897,000
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
Restricted Stock and Deferred Shares [Member]
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares)	385,000	410,000	401,000
Stock Options [Member]
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares)	285,000	469,000	492,000
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] | Restricted Stock and Deferred Shares [Member]
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares)	385,000	410,000	401,000
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)	285,000	469,000	492,000
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

X

- Definition

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Antidilution
-URI http://asc.fasb.org/extlink&oid=6505113

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Diluted Earnings Per Share
-URI http://asc.fasb.org/extlink&oid=6510752

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Contingent Stock Agreement
-URI http://asc.fasb.org/extlink&oid=6508534

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

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- Definition

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+ References

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