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Summary of Significant Accounting Policies - Construction in Progress (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Construction in progress	$ 161,625	$ 91,114
Glebe Road
Property, Plant and Equipment [Line Items]
Construction in progress	136,766	83,462
Ashbrook Marketplace
Property, Plant and Equipment [Line Items]
Construction in progress	10,016	0
Other
Property, Plant and Equipment [Line Items]
Construction in progress	$ 14,843	$ 7,652

X

- Definition

The current amount of expenditures for a real estate project that has not yet been completed.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.10)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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X

- 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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- Details

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