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

Earnings Per Share ("EPS") (Details 2)

Earnings Per Share ("EPS") (Details 2)	12 Months Ended
Earnings Per Share ("EPS") (Details 2)	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Restricted Stock [Member]
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	461,000	638,000	666,000
Weighted average conversion of common units
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	4,235,000	4,355,000	4,608,000
Weighted average conversion of convertible preferred units
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	176,000	176,000	176,000
Weighted average conversion of convertible preferred shares
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	434,000	434,000	434,000
Stock Options
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	772,000	712,000	653,000

- 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

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-Name Emerging Issues Task Force (EITF)

-Number 07-4

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Diluted Earnings Per Share

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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+ Details