Mortgage and Other Investing Receivables (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage and other investing receivables	$ 50,886	$ 53,663
Notes Receivable from City of Huntsville
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage and other investing receivables	47,878	44,055
Other investing loans receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage and other investing receivables	$ 3,008	$ 9,608

An amount classified as an investment activity representing an agreement for an unconditional promise by the maker to pay the Entity (holder) a definite sum of money at a future date, net of any write-downs taken for collection uncertainty on the part of the holder. Such amount may include accrued interest receivable in accordance with the terms of the note. The note also may contain provisions and related items including a discount or premium, payable on demand, secured, or unsecured, interest bearing or noninterest bearing, among a myriad of other features and characteristics. This amount does not include amounts related to receivables held-for-sale.

No definition available.

Name:	ofc_MortgageAndOtherInvestingReceivables
Namespace Prefix:	ofc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant