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Organization (Details 2)	6 Months Ended
	Jun. 30, 2011
Common Units
Forms of ownership in Operating Partnership and ownership percentage by the entity
Percentage ownership in operating partnership (as a percent)	94.00%
Number of trustees controlling additional common units	3
Additional percentage of common units controlled by trustees (as a percent)	5.00%
Preferred Units | Series G
Forms of ownership in Operating Partnership and ownership percentage by the entity
Percentage ownership in operating partnership (as a percent)	100.00%
Preferred Units | Series H
Forms of ownership in Operating Partnership and ownership percentage by the entity
Percentage ownership in operating partnership (as a percent)	100.00%
Preferred Units | Series I
Forms of ownership in Operating Partnership and ownership percentage by the entity
Percentage ownership in operating partnership (as a percent)	0.00%
Preferred Units | Series J
Forms of ownership in Operating Partnership and ownership percentage by the entity
Percentage ownership in operating partnership (as a percent)	100.00%
Preferred Units | Series K
Forms of ownership in Operating Partnership and ownership percentage by the entity
Percentage ownership in operating partnership (as a percent)	100.00%

X

- Definition

Additional percentage of the operating partnership's common units controlled by trustees, either directly or through ownership by other entities or family members.

+ Details

Name:	ofc_AdditionalPercentageOfCommonUnitsControlledByTrustees
Namespace Prefix:	ofc
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Represents the number of trustees who control common units in addition to those owned by the entity.

+ Details

Name:	ofc_NumberOfTrusteesControllingAdditionalCommonUnits
Namespace Prefix:	ofc
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Line items related to the percentage of classes of ownership in a subsidiary that are owned by the parent.

+ Details

Name:	ofc_OwnershipInSubsidiaryPercentageLineItems
Namespace Prefix:	ofc
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The number of units or percentage investment held by the managing member or general partner of the LLC or LP.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Practice Bulletin (PB)
-Number 14
-Paragraph 15
-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.

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055

+ Details

Name:	us-gaap_LimitedLiabilityCompanyLLCOrLimitedPartnershipLPManagingMemberOrGeneralPartnerOwnershipInterest
Namespace Prefix:	us-gaap
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration