Number of Properties Contributed

No definition available.

Name:	ofc_NumberofPropertiesContributed
Namespace Prefix:	ofc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Ownership Percentage Sold

+ References

No definition available.

+ Details

Name:	ofc_OwnershipPercentageSold
Namespace Prefix:	ofc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the total transaction value of operating property dispositions during the period.

+ References

No definition available.

+ Details

Name:	ofc_TransactionValueofOperatingPropertyDispositions
Namespace Prefix:	ofc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Value of property contributed in noncash investing and financing activities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4313-108586

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4332-108586

+ Details

Name:	us-gaap_ContributionOfProperty
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Gain (loss) included in earnings resulting from the sale of interest in projects.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=51717284&loc=d3e1361-107760

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=51719941&loc=d3e2941-110230

+ Details

Name:	us-gaap_GainLossOnSaleOfInterestInProjects
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

+ References

No definition available.

+ Details

Name:	us-gaap_ProceedsFromIssuanceOfDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

Name:	us-gaap_SubsequentEventLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RealEstatePropertiesAxis=ofc_SingletenantDataCentersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ofc_RealEstatePropertiesStatusAxis=ofc_OperatingOfficePropertiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Subsequent Event (Details) $ in Thousands		6 Months Ended
Subsequent Event (Details) $ in Thousands	Jul. 21, 2016 USD ($) Property	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)
Subsequent Event [Line Items]
Value of properties contributed		$ 22,600	$ 0
Subsequent Event \| Single-tenant data centers \| Operating office properties
Subsequent Event [Line Items]
Ownership percentage sold (percent)	50.00%
Number of properties contributed \| Property	6
Value of properties contributed	$ 147,600
Debt instrument, face amount	60,000
Transaction value of disposition of interest in properties	44,000
Gain on sale of interest in properties	$ 18,000