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Fair Value Measurements (Details 2) - USD ($) $ in Thousands | Sep. 30, 2018 | Dec. 31, 2017
--- | --- | ---
Assets: |  |
Marketable securities in deferred compensation plan | $ 4,346 | $ 4,616
Interest rate derivatives | 10,875 | 3,073
Corporate Office Properties, L.P. |  |
Assets: |  |
Interest rate derivatives | 10,875 | $ 3,073
Fair value measurement on a recurring basis |  |
Assets: |  |
Interest rate derivatives | 10,875 |
Total assets | 15,221 |
Liabilities: |  |
Deferred compensation plan liability | 4,346 |
Fair value measurement on a recurring basis | Mutual funds |  |
Assets: |  |
Marketable securities in deferred compensation plan | 4,298 |
Fair value measurement on a recurring basis | Other |  |
Assets: |  |
Marketable securities in deferred compensation plan | 48 |
Fair value measurement on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Assets: |  |
Total assets | 4,346 |
Fair value measurement on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Mutual funds |  |
Assets: |  |
Marketable securities in deferred compensation plan | 4,298 |
Fair value measurement on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other |  |
Assets: |  |
Marketable securities in deferred compensation plan | 48 |
Fair value measurement on a recurring basis | Significant Other Observable Inputs (Level 2) |  |
Assets: |  |
Interest rate derivatives | 10,875 |
Total assets | 10,875 |
Liabilities: |  |
Deferred compensation plan liability | 4,346 |
Fair value measurement on a recurring basis | Corporate Office Properties, L.P. |  |
Assets: |  |
Interest rate derivatives | 10,875 |
Fair value measurement on a recurring basis | Corporate Office Properties, L.P. | Significant Other Observable Inputs (Level 2) |  |
Assets: |  |
Interest rate derivatives | $ 10,875 |

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