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Business combination recognized identifiable assets acquired and liabilities assumed credit at settlement for notes receivable.

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Business combination recognized identifiable assets acquired and liabilities assumed mortgage debt repaid at settlement.

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Business combination recognized identifiable assets acquired and liabilities assumed net working capital assumed.

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Business combination recognized identifiable assets acquired and liabilities assumed unencumbered acquisition value excluding acquisition costs.

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Gains (losses) on promoted interest in unconsolidated real estate venture.

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Lease agreement term.

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Leasehold valuation credit.

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Leasehold valuation credit applied to development.

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Minimum floor area ratio required for realization of credit.

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Net gain (loss) on real estate venture transactions including real estate venture formation.

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Reimbursable leasehold valuation credit.

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Remaining leasehold valuation credit.

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Salaries including bonuses and benefits, capitalized during the period

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Sale of ownership interest percentage.

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- Definition

Area of a real estate property.

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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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Percentage of voting equity interests acquired at the acquisition date in the business combination.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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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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Amount of interest capitalized during the period.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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- Definition

Net rentable area for properties owned.

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- Definition

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

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- Definition

Net cash outflow for the allowance granted to lessee and/or direct costs incurred by lessor used to prepare the leased premises for tenant's occupancy; for costs that are essential to originating the lease and would not otherwise have been incurred without the lease agreement, including but not limited to, evaluating the lessee's credit condition, guarantees, and collateral and costs incurred in negotiating, processing, and executing the lease agreement; and for any commission(s) incurred.

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The cash outflow for acquisition of buildings (properties) whether for investment or use.

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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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The book value of investments in real estate joint ventures including direct and indirect investments.

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Amount, including tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value-added and excise.

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Percentage of subsidiary's or equity investee's stock owned by parent company after stock transaction.

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REAL ESTATE INVESTMENTS - Acquisitions (Textual) (Details) $ in Thousands								3 Months Ended									12 Months Ended			17 Months Ended
	Dec. 19, 2018 USD ($) ft²	Dec. 11, 2018 USD ($) ft² property	Jun. 29, 2018 USD ($) ft²	Mar. 22, 2018 USD ($)	Jan. 05, 2018 USD ($) ft²	Oct. 13, 2017 USD ($) ft²	Jul. 28, 2017 USD ($) ft²	Dec. 31, 2019 USD ($) ft² property	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2019 USD ($) ft² property	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2018 USD ($)
Business Acquisition [Line Items]
Internal direct construction costs capitalized related to development of properties and land holdings																	$ 7,431	$ 6,964	$ 6,063
Number of properties \| property								95									95
Area of real estate property \| ft²								16,711,387									16,711,387
Gain on promoted interest in unconsolidated real estate venture																	$ 0	28,283	0
Net gain from remeasurement of investment in real estate ventures																	11,639	142,233	80,526
Prepaid leasehold interests in land held for development, net								$ 39,592				$ 39,999				$ 0	39,592	39,999	0	$ 39,999
Capitalized transaction costs																	15,485	18,407	17,657
Net income (loss)								$ 16,676	$ 6,679	$ 6,112	$ 4,404	$ 120,792	$ (43,260)	$ 12,661	$ 43,956		$ 34,267	134,518	120,173
Office Properties
Business Acquisition [Line Items]
Number of properties \| property								86									86
Area of real estate property \| ft²								15,450,417									15,450,417
Seven Tower Bridge
Business Acquisition [Line Items]
Sale of ownership interest percentage					20.00%
Quarry Lake II
Business Acquisition [Line Items]
Rentable square feet \| ft²	120,559
Gross purchase value of office property	$ 39,500
Mortgage debt assumed repaid at settlement	0
Working capital obtained	368
Aggregate cash payment	$ 39,037
Service and other revenue																	$ 100
Net income (loss)																	100
DRA Austin Venture
Business Acquisition [Line Items]
Gross purchase value of office property		$ 535,100
Ownership percentage		50.00%
Number of properties \| property		12
Area of real estate property \| ft²		1,570,123
Investment in real estate venture		$ 14,600
Mortgage debt assumed repaid at settlement		115,461
Credit settlement for notes receivable provided to venture		130,700
Working capital obtained		24,865
Gain on promoted interest in unconsolidated real estate venture		28,300
Net gain from remeasurement of investment in real estate ventures		103,800
Aggregate cash payment		$ 117,348
Percentage of ownership interests		50.00%
Service and other revenue																	3,400
Net income (loss)																	$ 1,300
3025 JFK Boulevard
Business Acquisition [Line Items]
Lease agreement term			99 years														99 years
Prepaid leasehold interests in land held for development, net			$ 15,000
Capitalized transaction costs			300
3025 JFK Boulevard \| Other Assets
Business Acquisition [Line Items]
Leasehold valuation credit			5,600
3001-3003 and 3025 JFK Boulevard
Business Acquisition [Line Items]
Leasehold valuation credit applied to development			$ 2,400
Minimum floor area ratio required for realization of credit (sq. feet) \| ft²			1,200,000
Remaining leasehold valuation credit			$ 3,200
Reimbursable leasehold valuation credit			$ 3,200
3001-3003 JFK Boulevard
Business Acquisition [Line Items]
Lease agreement term				99 years
Prepaid leasehold interests in land held for development, net				$ 24,600
Capitalized transaction costs				$ 300
Four Tower Bridge
Business Acquisition [Line Items]
Ownership percentage					35.00%
Mortgage debt assumed repaid at settlement					$ 0
Working capital obtained					(1,379)
Aggregate cash payment					$ 0
Percentage of ownership interest after non-monetary exchange transaction					100.00%
Fair value of unencumbered acquisition related costs, to tangible and intangible assets and liabilities					$ 23,600
Service and other revenue																	$ 2,800
Net income (loss)																	300
Four Tower Bridge \| Conshohocken \| Pennsylvania
Business Acquisition [Line Items]
Area of real estate property \| ft²					86,021
Real estate property debt					$ 9,700
Bulletin Building
Business Acquisition [Line Items]
Rentable square feet \| ft²						282,709
Gross purchase value of office property						$ 35,000
Lease agreement term						99 years
Service and other revenue																1,200
Net income (loss)																$ 400
3000 Market Street
Business Acquisition [Line Items]
Gross purchase value of office property							$ 32,700
Service and other revenue																				800
Net income (loss)																				$ 500
3000 Market Street \| Office Properties
Business Acquisition [Line Items]
Area of real estate property \| ft²							58,587
Development
Business Acquisition [Line Items]
Capitalized interest																	$ 3,200	$ 3,600	$ 3,100