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Fair Value Measurements (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Assets and liabilities measured at fair value
Marketable securities in deferred compensation plan	$ 4,481	$ 4,616
Deferred compensation plan | Management
Assets and liabilities measured at fair value
Maximum percentage of participants' compensation which is deferrable (as a percent)	100.00%
Marketable securities in deferred compensation plan	$ 4,500

X

- Definition

Represents the maximum percentage of participants' compensation that is deferrable by participants under the deferred compensation plan.

+ References

No definition available.

+ Details

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Namespace Prefix:	ofc_
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Balance Type:	na
Period Type:	duration

X

- Definition

Carrying amount as of the balance sheet date of assets held under deferred compensation agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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X

- Details

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Namespace Prefix:
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X

- Details

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Namespace Prefix:
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Balance Type:
Period Type: