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Investments in Unconsolidated Joint Ventures Narrative (Details)
$ in Thousands

Jun. 27, 2019

USD ($)

ft²

May 28, 2019

USD ($)

Apr. 26, 2019

USD ($)

ft²

yr

Jan. 24, 2019

USD ($)

ft²

Jun. 30, 2019

USD ($)

Jun. 15, 2019

ft²

Dec. 31, 2018

USD ($)

Schedule of Equity Method Investments [Line Items]

Mortgage notes payable, net

$ 2,956,833

$ 2,964,572

Annapolis Junction Building Six [Member]

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

50.00%

Mortgage notes payable, net

$ 13,000

Debt Instrument, Basis Spread on Variable Rate

2.00%

Number of extensions

1

Extension Option (in years)

1

Debt instrument, borrowing capacity

$ 14,300

Net Rentable Area (in sf) | ft²

119,000

7750 Wisconsin Avenue LLC [Member]

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

50.00%

50.00%

^[1]

Construction Loan Facility Borrowing Capacity

$ 255,000

Debt Instrument, Basis Spread on Variable Rate

1.25%

Number of extensions

2

Extension Option (in years) | yr

1

Net Rentable Area (in sf) | ft²

734,000

The Hub on Causeway - Podium and One hundred Causeway [Member]

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

50.00%

Repayments of Construction Loans Payable

$ 30,000

Hub on Causeway - Podium [Member]

Schedule of Equity Method Investments [Line Items]

Net Rentable Area (in sf) | ft²

385,000

540 Madison Venture LLC [Member]

Schedule of Equity Method Investments [Line Items]

Ownership Percentage

60.00%

60.00%

^[2]

Contractual Sales Price

$ 310,300

Loans Assumed

$ 120,000

Debt Instrument, Basis Spread on Variable Rate

1.10%

Proceeds from Sale of Equity Method Investments

$ 178,700

Equity Method Investment, Realized Gain (Loss) on Disposal

$ 47,800

Net Rentable Area (in sf) | ft²

284,000

Company's Share [Member] | 540 Madison Venture LLC [Member]

Schedule of Equity Method Investments [Line Items]

Proceeds from Sale of Equity Method Investments

$ 107,100

[1]	This entity is a VIE (See Note 2).
[2]	The property was sold on June 27, 2019. As of June 30, 2019, the investment is comprised of undistributed cash. See note below for additional details.

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