Total anticipated cost of investment in assets including but not limited to assets under construction.

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Number of equity method investments

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The ceiling amount as of the balance sheet date that the entity must expend to satisfy the terms of disclosed arrangements (excluding long-term commitments) in which the entity must commit resources to supply goods or services to one or more customers.

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No definition available.

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The aggregate costs related to goods produced and sold and services rendered by an entity during the reporting period. This excludes costs incurred during the reporting period related to financial services rendered and other revenue generating activities.

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For an unclassified balance sheet, this element represents costs incurred by the lessor that are (a) costs to originate a lease incurred in transactions with independent third parties that (i) result directly from and are essential to acquire that lease and (ii) would not have been incurred had that leasing transaction not occurred and (b) certain costs directly related to specified activities performed by the lessor for that lease. Those activities are: evaluating the prospective lessee's financial condition; evaluating and recording guarantees, collateral, and other security arrangements; negotiating lease terms; preparing and processing lease documents; and closing the transaction. This amount is before considering accumulated amortization representing the periodic charge to earnings to recognize the deferred costs over the term of the related lease.

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

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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Amount of loss contingency liability.

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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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Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

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The floor amount as of the balance sheet date that the entity must expend to satisfy the terms of disclosed arrangements (excluding long-term commitments) in which the entity must commit resources to supply goods or services to one or more customers.

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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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No definition available.

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Commitments and Contingencies (Other) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) ft² bldg	Dec. 31, 2017 USD ($) ft²	Dec. 31, 2016 USD ($)	Jun. 30, 2014 USD ($) ft² investment
Supply Commitment [Line Items]
Letter of credit obligations	$ 8,300
Number of buildings (in buildings) \| bldg	72
Development in progress	$ 462,572	$ 294,009
Deferred leasing costs in development	189,178	160,759
Costs incurred to date	134,825	$ 85,805	$ 12,165
Land, Buildings and Improvements \| Supply Commitment
Supply Commitment [Line Items]
Remaining amount committed or obligated to pay	$ 13,000
Construction in Progress \| Supply Commitment
Supply Commitment [Line Items]
Number of buildings (in buildings) \| bldg	29
Leaseable square feet (in sqft) \| ft²	8,200,000
Total anticipated development cost	$ 735,000
Deferred leasing costs in development	$ 13,200
Construction in Progress \| Equity Method Investments \| Supply Commitment
Supply Commitment [Line Items]
Number of buildings (in buildings) \| bldg	2
Total anticipated development cost	$ 235,800
Leasehold Improvements \| Supply Commitment
Supply Commitment [Line Items]
Remaining maximum amount committed for tenant improvements	17,800
American Water Works, Inc \| Building and Building Improvements
Supply Commitment [Line Items]
Costs incurred to date	159,200
American Water Works, Inc \| Building and Building Improvements \| Supply Commitment
Supply Commitment [Line Items]
Fee development commitment	$ 170,900
Liberty Property 18th & Arch \| Philadelphia
Supply Commitment [Line Items]
Number of equity method investments (in investments) \| investment				2
Liberty Property 18th & Arch \| Philadelphia \| Building and Building Improvements
Supply Commitment [Line Items]
Leaseable square feet (in sqft) \| ft²	250,000	1,100,000
Total anticipated development cost	$ 136,100	$ 599,600
Liberty Property 18th & Arch \| Philadelphia \| Construction in Progress
Supply Commitment [Line Items]
Leaseable square feet (in sqft) \| ft²				1,300,000
Total anticipated development cost	$ 225,500			$ 961,200
Other Joint Ventures \| Philadelphia \| Building and Building Improvements
Supply Commitment [Line Items]
Number of buildings (in buildings) \| bldg	1
Leaseable square feet (in sqft) \| ft²	48,000
Other Liabilities \| Guarantee Obligations \| Liberty Property 18th & Arch \| Philadelphia
Supply Commitment [Line Items]
Loss contingency accrual	$ 67,300	$ 5,600