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Subsequent Events (Details) (USD $) | 0 Months Ended | 6 Months Ended |  | 0 Months Ended | 6 Months Ended |  | 0 Months Ended |  |  | 6 Months Ended | 0 Months Ended | 6 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Mar. 19, 2013 | Jun. 30, 2013 | Jun. 30, 2012 | Dec. 31, 2012 | Mar. 19, 2013 Corporate Office Properties, L.P. | Jun. 30, 2013 Corporate Office Properties, L.P. | Jun. 30, 2012 Corporate Office Properties, L.P. | Jul. 12, 2013 Corporate Office Properties, L.P. Subsequent Event | Jul. 16, 2013 Amendment to Revolving Credit Facility Revolving Credit Facility Subsequent Event | Jul. 16, 2013 Amendment to Revolving Credit Facility London Interbank Offered Rate (LIBOR) Revolving Credit Facility Subsequent Event | Jun. 30, 2013 Amendment to Revolving Credit Facility London Interbank Offered Rate (LIBOR) Revolving Credit Facility Subsequent Event | Jun. 30, 2013 Common Shares | Jul. 12, 2013 Common Shares Subsequent Event | Jun. 30, 2013 Common Shares Corporate Office Properties, L.P. | Jun. 30, 2012 Common Shares Corporate Office Properties, L.P. | Jun. 30, 2013 Term Loan Facility Amendment to Term Loan Facilities Unsecured Debt Subsequent Event | Jul. 16, 2013 Term Loan Facility Amendment to Term Loan Facilities London Interbank Offered Rate (LIBOR) Subsequent Event | Jun. 30, 2013 Term Loan Facility Amendment to Term Loan Facilities London Interbank Offered Rate (LIBOR) Subsequent Event
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares issued to the public (in shares) | 4,485,000 |  |  |  | 4,485,000 |  |  |  |  |  |  |  | 1,500,000.0 | 4,485,000 |  |  |  |
Issuance of stock, weighted average price per share |  |  |  |  |  |  |  |  |  |  |  |  | $ 26.05 |  |  |  |  |
Shares issued to the public (in dollars) | $ 118,100,000 | $ 117,913,000 | $ 165,665,000 |  |  | $ 117,913,000 | $ 165,665,000 |  |  |  |  | $ 45,000 | $ 38,500,000 | $ 117,913,000 | $ (6,835,000) |  |  |
Payments of Stock Issuance Costs |  |  |  |  |  |  |  |  |  |  |  |  | 586,000 |  |  |  |  |
Common Stock, Shares, Issued |  | 85,845,403 |  | 80,952,986 |  |  |  | 1,500,000.0 |  |  |  |  |  |  |  |  |  |
Debt instrument, extension option, term |  |  |  |  |  |  |  |  | 1 year |  |  |  |  |  |  |  |  |
Line of credit facility, extension fee percentage |  |  |  |  |  |  |  |  | 0.15% |  |  |  |  |  |  |  |  |
Variable rate, spread (as a percent) |  |  |  |  |  |  |  |  |  | 1.75% | 0.975% |  |  |  |  |  | 1.10% | 2.00%
Debt instrument, face amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 550,000,000 |  |

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- Definition Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.29) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 30 -Article 5 + Details
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