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Equity (Details) (USD $) | 0 Months Ended | 6 Months Ended | 0 Months Ended | 6 Months Ended
--- | --- | --- | --- | ---
Mar. 19, 2013 | Jun. 30, 2013 | Jun. 30, 2012 | Apr. 22, 2013 Series J Preferred Stock | Mar. 19, 2013 Corporate Office Properties, L.P. | Jun. 30, 2013 Corporate Office Properties, L.P. | Jun. 30, 2012 Corporate Office Properties, L.P.
Class of Stock [Line Items] |  |  |  |  |  |  |
Dividend rate |  |  |  | 7.625% |  |  |
Redemption price per share |  |  |  | $ 25 |  |  |
Stock redeemed or called during period, value |  | $ 84,750,000 |  | $ 84,800,000 |  | $ 84,750,000 |
Issuance costs associated with redeemed preferred shares |  |  |  | 2,900,000 |  |  |
Common Shares |  |  |  |  |  |  |
Shares issued to the public | 4,485,000 |  |  |  | 4,485,000 |  |
Shares issued to the public (in dollars per share) | $ 26.34 |  |  |  |  |  |
Public Offering, Proceeds After Underwriter Discounts But Before Offering Expenses | $ 118,100,000 | $ 117,913,000 | $ 165,665,000 |  |  | $ 117,913,000 | $ 165,665,000
Number of operating parterships units converted into common shares (in units) |  | 279,019 | 54,550 |  |  |  |
Number of common shares for each converted common unit (in shares) |  | 1 |  |  |  |  |

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- Definition The excess of (1) fair value of the consideration transferred to the holders of the preferred stock over (2) the carrying amount of the preferred stock in the registrant's balance sheet, during the accounting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section S99 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6802175&loc=d3e42851-122695 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Emerging Issues Task Force (EITF) -Number D-42 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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- Definition The price per share at which the preferred stock of an entity that has priority over common stock in the distribution of dividends and in the event of liquidation of the entity is redeemed or may be called at. The redemption features of this preferred stock are solely within the control of the issuer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21564-112644 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21475-112644 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21488-112644 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 129 -Paragraph 7 -Subparagraph a -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 129 -Paragraph 4, 8 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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