Quarterly report pursuant to Section 13 or 15(d)

Investing Receivables (Details)

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Investing Receivables (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Investing receivables $ 52,814us-gaap_NotesReceivableNet $ 52,147us-gaap_NotesReceivableNet
Notes Receivable from City of Huntsville    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Investing receivables 49,814us-gaap_NotesReceivableNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ofc_NotesReceivableFromCityOfHuntsvilleMember
49,147us-gaap_NotesReceivableNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ofc_NotesReceivableFromCityOfHuntsvilleMember
Notes Receivable from City of Huntsville | LW Redstone Company, LLC    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Stated interest rate (as a percent) 9.95%ofc_NoteReceivableTermsInterestRate
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ofc_NotesReceivableFromCityOfHuntsvilleMember
/ dei_LegalEntityAxis
= ofc_LwRedstoneCompanyLlcMember
 
Other investing loans receivable    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Investing receivables $ 3,000us-gaap_NotesReceivableNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_LoansAndFinanceReceivablesMember
$ 3,000us-gaap_NotesReceivableNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_LoansAndFinanceReceivablesMember