Segment Information - Real Estate Investments, at Cost of Company's Reportable Segments (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Operating properties	$ 3,650,521	$ 4,006,459
Assets held for sale - real estate investments	327,286	0
Operating Properties	3,977,807	4,006,459
Right of use asset - operating leases, net	21,315	21,656
Construction-in-progress	235,475	180,718
Land held for development	112,420	96,124
Prepaid leasehold interests in land held for development, net	39,389	39,592
Philadelphia CBD
Segment Reporting Information [Line Items]
Operating properties	1,384,550	1,726,299
Pennsylvania Suburbs
Segment Reporting Information [Line Items]
Operating properties	987,069	1,003,890
Austin, Texas
Segment Reporting Information [Line Items]
Operating properties	722,710	721,255
Metropolitan Washington, D.C.
Segment Reporting Information [Line Items]
Operating properties	469,091	468,035
Other
Segment Reporting Information [Line Items]
Operating properties	87,101	$ 86,980
Held-for-sale
Segment Reporting Information [Line Items]
Assets held for sale - real estate investments	327,286
Construction-in-progress	1,881
Land held for development	7,349
Philadelphia - Office \| Held-for-sale
Segment Reporting Information [Line Items]
Assets held for sale - real estate investments	327,286
Construction-in-progress	1,881
Land held for development	$ 0

Real Estate Investment Property Held For Use and Sale

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

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Carrying amount of land available for development.

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- Definition

Amount of lessee's right to use underlying asset under operating lease.

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Carrying amount as of the balance sheet date of expenditures made in advance of when the economic benefit of the cost will be realized, and which will be expensed in future periods with the passage of time or when a triggering event occurs.

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Carrying amount as of the balance sheet date of investments in land and buildings held for sale, excluding real estate considered to be inventory of the entity.

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Amount of real estate investment property which may include the following: (1) land available-for-sale; (2) land available-for-development; (3) investments in building and building improvements; (4) tenant allowances; (5) developments in-process; (6) rental properties; and (7) other real estate investments.

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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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