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Properties, net (Details) (USD $)			6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2014 Greater Philadelphia	Jun. 30, 2014 Operating properties, net	Dec. 31, 2013 Operating properties, net	Jun. 30, 2014 Operating properties, net Land	Dec. 31, 2013 Operating properties, net Land	Jun. 30, 2014 Operating properties, net Buildings and improvements	Dec. 31, 2013 Operating properties, net Buildings and improvements
Investments in real estate
Gross						$ 433,362,000	$ 430,472,000	$ 2,946,094,000	$ 2,869,870,000
Less: accumulated depreciation				(655,214,000)	(597,649,000)
Operating properties, net	2,724,242,000	2,702,693,000
Depreciation Expense on Reclassified Assets			$ 12,900,000

X

- Definition

Additional depreciation expense recognized resulting from a change in the useful life of the disclosed asset.

+ References

No definition available.

+ Details

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Namespace Prefix:	ofc_
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X

- Definition

Amount, before accumulated depreciation, of real estate investments for entities with a substantial portion of business acquiring and holding investment real estate.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 10

-Section S99

-Paragraph 6

-Subparagraph (SX 210.5-04.(c) Schedule III)

-URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674



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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 28

-Article 12



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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph c

-Subparagraph Schedule III

-Article 5



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 970

-SubTopic 360

-Section S99

-Paragraph 1

-Subparagraph (SX 210.12-28.4)

-URI http://asc.fasb.org/extlink&oid=6590653&loc=d3e638233-123024

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X

- Definition

The cumulative amount of depreciation for real estate property held for investment purposes.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.1(3))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910



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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 7

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- Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
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X

- Definition

Carrying amount of income producing properties held for rental.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.1(d))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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