Real Estate Properties - Schedule of Joint Ventures (Details) $ in Thousands	9 Months Ended
Sep. 30, 2018 USD ($) ft² property joint_venture building
Real Estate [Line Items]
Number of joint ventures \| joint_venture	2
Number of Properties \| property	105
Number of buildings \| building	164
Unconsolidated Joint Ventures
Real Estate [Line Items]
Investment at carrying value	$ 45,161
Number of buildings \| building	3
Square Feet (in square feet) \| ft²	443,867
Interest rate (as a percent)	3.9339%
Principal Balance	$ 82,000
Unamortized basis difference	$ 8,565
Unconsolidated Joint Ventures \| Prosperity Metro Plaza
Real Estate [Line Items]
GOV Ownership	51.00%
Investment at carrying value	$ 24,821
Number of buildings \| building	2
Square Feet (in square feet) \| ft²	328,456
Interest rate (as a percent)	4.09%
Principal Balance	$ 50,000
Unconsolidated Joint Ventures \| 1750 H Street, NW
Real Estate [Line Items]
GOV Ownership	50.00%
Investment at carrying value	$ 20,340
Number of buildings \| building	1
Square Feet (in square feet) \| ft²	115,411
Interest rate (as a percent)	3.69%
Principal Balance	$ 32,000

The number of buildings owned as of the balance sheet date.

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- Definition

Number Of Joint Ventures

+ References

No definition available.

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- Definition

Amount of contractual principal due at origination of mortgage loan within investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 12
-Paragraph Column F
-Subsection 29

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29(Column F))
-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

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- Definition

Area of a real estate property.

+ References

No definition available.

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Difference between amount at which an investment accounted for under the equity method of accounting is carried (reported) on the balance sheet and amount of underlying equity in net assets the reporting Entity has in the investee.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

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- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

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This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 280
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-Section 50
-Paragraph 25
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-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8813-108599

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-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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The number of real estate properties owned as of the balance sheet date.

+ References

No definition available.

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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.

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