Area of land held.

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For an unclassified balance sheet, amounts due from related parties including affiliates, employees, joint ventures, officers and stockholders, immediate families thereof, and pension funds.

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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.

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Gross amount of debt extinguished.

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No definition available.

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The difference between the carrying value and the sale price of real estate or properties that were intended to be sold or held for capital appreciation or rental income. This element refers to the gain (loss) included in earnings and not to the cash proceeds of the sale. This element is a noncash adjustment to net income when calculating net cash generated by operating activities using the indirect method.

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Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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The net gain (loss) resulting from sales and other disposals of real estate owned for investment purposes.

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The charge against earnings in the period to reduce the carrying amount of real property to fair value.

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Revenue, comprised of base and incentive revenue derived from the management of joint ventures, managing third-party properties, or another entity's operations.

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Net rentable area for properties owned.

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

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The cash inflow from the sale of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale.

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Cash received from the sale of real estate that is held for investment, that is, it is part of an investing activity during the period.

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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.

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Investments in Unconsolidated Joint Ventures (Liberty Washington, LP) (Details) ft² in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) ft² a bldg properties	Dec. 31, 2016 USD ($) ft² a properties	Dec. 31, 2015 USD ($) ft² properties
Schedule of Equity Method Investments [Line Items]
Number of properties \| bldg	37
Acres of developable land \| a	9
Gain (loss) on debt extinguishment	$ (49)	$ (27,099)	$ 0
Gain (loss) on sale of properties	114,965	219,270	100,314
Gross proceeds	379,139	1,192,918	530,440
Impairment - real estate assets	$ 3,946	$ 3,879	$ 17,215
Discontinued Operations, Disposed of by Sale [Member]
Schedule of Equity Method Investments [Line Items]
Number of properties \| bldg	2
Northern Virginia and Washington DC [Member] \| Liberty Washington, LP [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage	25.00%
Building and Building Improvements [Member] \| Northern Virginia and Washington DC [Member] \| Liberty Washington, LP [Member]
Schedule of Equity Method Investments [Line Items]
Leaseable square feet \| ft²	451
Building and Building Improvements [Member] \| Northern Virginia and Washington DC [Member] \| Office Building [Member] \| Liberty Washington, LP [Member]
Schedule of Equity Method Investments [Line Items]
Number of properties \| properties	2
Joint venture, 2016 sales current quarter [Member] \| Building and Building Improvements [Member] \| Liberty Washington, LP [Member] \| Discontinued Operations, Disposed of by Sale [Member]
Schedule of Equity Method Investments [Line Items]
Number of properties \| properties		12
Leaseable square feet \| ft²		1,200
Proceeds from sale of property		$ 187,200
Joint venture, 2016 sales current quarter [Member] \| Land and Land Improvements [Member] \| Liberty Washington, LP [Member] \| Discontinued Operations, Disposed of by Sale [Member]
Schedule of Equity Method Investments [Line Items]
Acres of developable land \| a		6.0
Joint venture, 2016 transfer to lender [Member] \| Building and Building Improvements [Member] \| Liberty Washington, LP [Member] \| Discontinued Operations, Disposed of by Means Other than Sale [Member]
Schedule of Equity Method Investments [Line Items]
Number of properties \| properties		6
Leaseable square feet \| ft²		698
Joint venture sales, 2015 [Member] \| Building and Building Improvements [Member] \| Northern Virginia [Member] \| Liberty Washington, LP [Member] \| Not Discontinued Operations [Member]
Schedule of Equity Method Investments [Line Items]
Number of properties \| properties			1
Leaseable square feet \| ft²			80
Gross proceeds			$ 5,000
Mortgages [Member] \| Joint venture, 2016 transfer to lender [Member] \| Building and Building Improvements [Member] \| Liberty Washington, LP [Member] \| Discontinued Operations, Disposed of by Means Other than Sale [Member]
Schedule of Equity Method Investments [Line Items]
Extinguishment of debt		$ 112,500
Gain (Loss) on Investments [Member] \| Northern Virginia [Member] \| Liberty Washington, LP [Member]
Schedule of Equity Method Investments [Line Items]
Impairment - real estate assets			56,800
Equity Method Investee [Member] \| DC Metro [Member] \| Liberty Washington, LP [Member]
Schedule of Equity Method Investments [Line Items]
Impairment - real estate assets	$ 15,900
General Partner [Member] \| Gain (Loss) on Investments [Member] \| Northern Virginia [Member] \| Liberty Washington, LP [Member]
Schedule of Equity Method Investments [Line Items]
Impairment - real estate assets			11,500
General Partner [Member] \| Gain (Loss) on Investments [Member] \| Joint venture, 2016 sales current quarter [Member] \| Building and Building Improvements [Member] \| Liberty Washington, LP [Member] \| Discontinued Operations [Member]
Schedule of Equity Method Investments [Line Items]
Gains on sale of land and building		6,000
General Partner [Member] \| Gain (Loss) on Investments [Member] \| Mortgages [Member] \| Joint venture, 2016 transfer to lender [Member] \| Building and Building Improvements [Member] \| Liberty Washington, LP [Member] \| Discontinued Operations [Member]
Schedule of Equity Method Investments [Line Items]
Gain (loss) on debt extinguishment		4,200
Liberty Washington, LP [Member] \| Equity Method Investee [Member] \| Northern Virginia and Washington DC [Member]
Schedule of Equity Method Investments [Line Items]
Management fees revenue	1,100	2,000	$ 4,800
Prepaid Expenses and Other Current Assets [Member] \| Liberty Washington, LP [Member] \| Equity Method Investee [Member] \| Northern Virginia and Washington DC [Member]
Schedule of Equity Method Investments [Line Items]
Due from related parties	316	$ 322
Investments in and advances to unconsolidated joint ventures [Member] \| General Partner [Member] \| Equity Method Investee [Member] \| DC Metro [Member] \| Liberty Washington, LP [Member]
Schedule of Equity Method Investments [Line Items]
Impairment - real estate assets	$ 4,000