Mortgage and Other Investing Receivable (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage and other investing receivables	$ 53,663	$ 35,798
Notes receivable from City of Huntsville
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage and other investing receivables	44,055	35,654
Mortgage loans receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage and other investing receivables	$ 9,608	$ 144
Number of mortgage loans receivable	1

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