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Summary of Significant Accounting Policies (Details 5) - USD ($) $ in Thousands |  | 12 Months Ended |
--- | --- | --- | ---
Jan. 01, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Jan. 01, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |
Deferred non-incremental lease cost |  | $ 1,200 | $ 1,100 | $ 1,100 |
Cumulative Distributions in Excess of Net Income [Member] |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |
Cumulative effect of accounting change for adoption of hedge accounting guidance |  |  | (276) |  |
Cumulative Distributions in Excess of Net Income [Member] | Accounting Standards Update 2017-12 [Member] |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |
Cumulative effect of accounting change for adoption of hedge accounting guidance |  |  |  |  | $ (276)
Accumulated Other Comprehensive Income (Loss) [Member] |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |
Cumulative effect of accounting change for adoption of hedge accounting guidance |  |  | 276 |  |
Accumulated Other Comprehensive Income (Loss) [Member] | Accounting Standards Update 2017-12 [Member] |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |
Cumulative effect of accounting change for adoption of hedge accounting guidance |  |  |  |  | 276
Accumulated Other Comprehensive Income (Loss) [Member] | Corporate Office Properties, L.P. [Member] |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |
Cumulative effect of accounting change for adoption of hedge accounting guidance |  |  | 276 |  |
Accumulated Other Comprehensive Income (Loss) [Member] | Corporate Office Properties, L.P. [Member] | Accounting Standards Update 2017-12 [Member] |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |
Cumulative effect of accounting change for adoption of hedge accounting guidance |  |  |  |  | 276
Common Shares [Member] | Corporate Office Properties, L.P. [Member] |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |
Cumulative effect of accounting change for adoption of hedge accounting guidance |  |  | $ (276) |  |
Common Shares [Member] | Corporate Office Properties, L.P. [Member] | Accounting Standards Update 2017-12 [Member] |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |
Cumulative effect of accounting change for adoption of hedge accounting guidance |  |  |  |  | $ (276)
Scenario, Forecast [Member] | Right-of-use Assets [Member] | Accounting Standards Update 2016-02 [Member] | Minimum [Member] |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |
Effect of new accounting principle | $ 14,000 |  |  |  |
Scenario, Forecast [Member] | Right-of-use Assets [Member] | Accounting Standards Update 2016-02 [Member] | Maximum [Member] |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |
Effect of new accounting principle | 19,000 |  |  |  |
Scenario, Forecast [Member] | Lease Liability [Member] | Accounting Standards Update 2016-02 [Member] | Minimum [Member] |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |
Effect of new accounting principle | 14,000 |  |  |  |
Scenario, Forecast [Member] | Lease Liability [Member] | Accounting Standards Update 2016-02 [Member] | Maximum [Member] |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |
Effect of new accounting principle | $ 19,000 |  |  |  |

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