| Real Estate Joint Ventures - Narrative (Details) - property | Jun. 30, 2021 | Jun. 02, 2021 | 
|---|---|---|
| B RE COPT DC JV III LLC | ||
| Real Estate [Line Items] | ||
| Nominal Ownership % | 10.00% | 10.00% | 
| Disposed of by sale | Data Center Shells in Northern Virginia | ||
| Real Estate [Line Items] | ||
| Ownership percentage sold | 90.00% | |
| Number of real estate properties sold | 2 | 
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- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
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