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Equity (Details) (USD $) In Millions, except Share data, unless otherwise specified | 3 Months Ended
--- | ---
Mar. 31, 2015 | Mar. 31, 2014
Class of Stock [Line Items] |  |
Number of operating partnerships units converted into common shares (in units) | 158,000 us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits | 48,498 us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits
Common Shares |  |
Class of Stock [Line Items] |  |
Shares issued to the public (in units/ shares) | 890,241 us-gaap_StockIssuedDuringPeriodSharesNewIssues / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |
Weighted average price per share of stock issued | 30.29 ofc_IssuanceofStockWeightedAveragePricePerShare / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |
Net proceeds of stock issuance | 26.6 ofc_ProceedsfromIssuanceofCommonStockNetofIssuanceCosts / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |
Commission costs | 0.4 us-gaap_PaymentsOfStockIssuanceCosts / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |
Remaining capacity under ATM Plan | 84.0 ofc_AtMarketStockOfferingProgramEstablishedRemainingCapacity / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |
Corporate Office Properties, L.P. | Common Shares |  |
Class of Stock [Line Items] |  |
Shares issued to the public (in units/ shares) | 890,241 us-gaap_StockIssuedDuringPeriodSharesNewIssues / dei_LegalEntityAxis = us-gaap_SubsidiariesMember / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |

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