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Information by Business Segment (Details 4) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
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Reconciliation of segment assets to total assets |  |  |
Total COPT consolidated assets | $ 3,578,484 | $ 3,780,885 |
Segment assets [Member] |  |  |
Reconciliation of segment assets to total assets |  |  |
Total COPT consolidated assets | 3,011,284 | 3,004,247 | $ 3,265,469
Non-operating property assets [Member] |  |  |
Reconciliation of segment assets to total assets |  |  |
Total COPT consolidated assets | 411,041 | 418,171 |
Other assets [Member] |  |  |
Reconciliation of segment assets to total assets |  |  |
Total COPT consolidated assets | $ 156,159 | $ 358,467 |

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