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Properties, Net (Details 4) ft² in Thousands, $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2018 USD ($) ft² Property | Dec. 31, 2018 USD ($) ft² Property | Dec. 31, 2017 USD ($) ft² Property | Dec. 31, 2016 USD ($) ft² buillding Property
Construction Activities [Line Items] |  |  |  |
Impairment losses | $ |  | $ 2,367 | $ 15,123 | $ 101,391
Fort Meade/BW Corridor [Member] |  |  |  |
Construction Activities [Line Items] |  |  |  |
Impairment losses | $ | $ 2,400 |  |  |
Newly-constructed properties placed in service [Member] |  |  |  |
Construction Activities [Line Items] |  |  |  |
Square footage of real estate properties (in square feet) | ft² | 666 | 666 | 1,100 | 639
Number of real estate properties | 6 | 6 | 8 | 6
Newly-constructed properties placed in service, partially operational [Member] |  |  |  |
Construction Activities [Line Items] |  |  |  |
Number of real estate properties | 2 | 2 |  |
Newly redeveloped properties placed In service [Member] |  |  |  |
Construction Activities [Line Items] |  |  |  |
Square footage of real estate properties (in square feet) | ft² | 22 | 22 | 94 | 61
Number of real estate properties | 1 | 1 |  | 3
Properties Under Construction or Contractually Committed, Partially Operational [Member] |  |  |  |
Construction Activities [Line Items] |  |  |  |
Number of real estate properties | 2 | 2 |  |
Properties under Construction or Contractually Commited for Construction [Member] |  |  |  |
Construction Activities [Line Items] |  |  |  |
Square footage of real estate properties (in square feet) | ft² | 1,100 | 1,100 |  |
Number of real estate properties | 9 | 9 |  |
Properties under redevelopment [Member] |  |  |  |
Construction Activities [Line Items] |  |  |  |
Square footage of real estate properties (in square feet) | ft² | 106 | 106 |  |
Number of real estate properties | 1 | 1 |  |

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- Definition Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=109226348&loc=d3e2420-110228 + Details
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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. + References No definition available. + Details
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- Definition The number of real estate properties owned as of the balance sheet date. + References No definition available. + Details
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