Investment in Unconsolidated Joint Ventures (Narrative) (Details) $ in Thousands								12 Months Ended
		Dec. 31, 2021 USD ($)		Dec. 14, 2021 USD ($) ft² loanExtension yr Rate	Sep. 01, 2021 USD ($) ft²	Aug. 31, 2021 USD ($) ft² years loanExtension	Mar. 30, 2021 USD ($) ft²	Dec. 31, 2021 USD ($)		Dec. 31, 2020 USD ($)		Dec. 31, 2019 USD ($)	Dec. 15, 2021	Oct. 29, 2021 ft²	Jun. 11, 2021 ft²	Feb. 25, 2021 ft²
Schedule of Equity Method Investments [Line Items]
Mortgage notes payable, net		$ 3,267,914						$ 3,267,914		$ 2,909,081
Debt Instrument, Basis Spread on Variable Rate		0.775%
Proceeds from Sale of Equity Method Investments								17,789		0		$ 0
Payments to Acquire Equity Method Investments								98,152		172,436		87,392
Income (Loss) from Equity Method Investments								(2,570)		(85,110)		46,592
Capital distributions from unconsolidated joint ventures								122		55,298		136,807
Proceeds from sales of real estate								179,887		519,303		90,824
Repayments of Secured Debt								$ 832,296		$ 17,168		46,173
7750 Wisconsin Avenue [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage														50.00%
Net Rentable Area (in sf) | ft²														733,000
360 Park South Avenue
Schedule of Equity Method Investments [Line Items]
Ownership Percentage													42.21%
Net Rentable Area (in sf) | ft²				450,000
Number of floors				20
number of investors													2
Debt - Total loan amount				$ 220,000
360 Park South Avenue | Adjustable Rate Loans
Schedule of Equity Method Investments [Line Items]
Debt Instrument, Basis Spread on Variable Rate | Rate				2.40%
Number of extensions | loanExtension				2
Extension Option (in years) | yr				1
Debt - Total loan amount				$ 220,000
Proceeds from Issuance of Debt				$ 202,000
Gateway Commons Complex [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		50.00%	[1]					50.00%	[1]	55.00%						54.00%
Gateway Commons Complex [Member] | Scenario, Plan
Schedule of Equity Method Investments [Line Items]
Ownership Percentage										50.00%
Gateway Commons Complex [Member] | Scenario, Plan | 751 Gateway
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		49.00%						49.00%
Gateway Commons Complex prior to deferred contribution [Member] [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		50.00%						50.00%		55.00%
Platform 16
Schedule of Equity Method Investments [Line Items]
Ownership Percentage	[2]	55.00%						55.00%
Annapolis Junction NFM, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage							50.00%			50.00%	[3]
Contractual Sales Price							$ 65,900
Proceeds from Sale of Equity Method Investments							17,800
Capital distributions from unconsolidated joint ventures							5,800
Gain on Sale of Investments							10,300	$ 10,300
Repayments of Secured Debt							$ 15,100
Annapolis Junction NFM, LLC [Member] | Annapolis Junction Building Six and Seven | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Net Rentable Area (in sf) | ft²							247,000
100 Causeway Street [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		50.00%						50.00%
100 Causeway Street [Member] | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Ownership Percentage															50.00%
Net Rentable Area (in sf) | ft²															634,000
Safeco Plaza REIT LLC
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		33.67%	[4]		33.67%			33.67%	[4]
Mortgage notes payable, net					$ 250,000
Net Rentable Area (in sf) | ft²					765,000
Payments to Acquire Equity Method Investments					$ 72,600
Debt Instrument, Description of Variable Rate Basis					variable rate equal to the greater of (x) 2.35% or (y) LIBOR plus 2.20% per annum
Aggregate purchase price					$ 460,100
Number of floors					50
number of investors					2
Acquisition Costs, Period Cost					$ 4,900
Podium Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		50.00%				50.00%		50.00%
Mortgage notes payable, net						$ 174,300
Debt Instrument, Basis Spread on Variable Rate						2.25%
Net Rentable Area (in sf) | ft²						382,000
Number of extensions | loanExtension						2
Extension Option (in years) | years						1
360 PAS Holdco LLC
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		42.21%	[5]					42.21%	[5]				42.21%
number of investors													2
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Mortgage notes payable, net		$ 3,214,961						$ 3,214,961		$ 2,637,911
Income (Loss) from Equity Method Investments								(2,570)		(85,110)		46,592
Impairment loss on investment								0		60,524	[6]	0
Gain on Sale of Investments								$ 10,257	[7]	0		$ 0
Unconsolidated Joint Ventures [Member] | Dock 72 [Member]
Schedule of Equity Method Investments [Line Items]
Impairment loss on investment										$ 60,500
Construction in Progress | Gateway Commons Complex [Member] | 751 Gateway | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Net Rentable Area (in sf) | ft²																231,000
Company's Share [Member] | Safeco Plaza REIT LLC
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		33.00%						33.00%
Company's Share [Member] | Safeco Partner Entity One [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		1.00%						1.00%
Company's Share [Member] | Safeco Partner Entity Two
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		1.00%						1.00%
Company's Share [Member] | 360 Park Avenue South Partners Entity Two
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		1.00%						1.00%					1.00%
Company's Share [Member] | 360 Park Avenue South Partners Entity
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		1.00%						1.00%					1.00%
Company's Share [Member] | 360 PAS Holdco LLC (indirect ownership)
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		5.837%						5.837%					5.837%
Company's Share [Member] | 360 PAS Holdco LLC
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		35.79%						35.79%					35.79%
Institutional investor number one | Safeco Plaza REIT LLC
Schedule of Equity Method Investments [Line Items]
Ownership Percentage					33.165%
Payments to Acquire Equity Method Investments					$ 71,900
Institutional investor number two | Safeco Plaza REIT LLC
Schedule of Equity Method Investments [Line Items]
Ownership Percentage					33.165%
Payments to Acquire Equity Method Investments					$ 71,900
Institutional investors | 360 PAS Holdco LLC
Schedule of Equity Method Investments [Line Items]
Ownership Percentage													58.00%

[1] As a result of the partner’s deferred contribution, the Company owned an approximately 50% and 55% interest in the joint venture at December 31, 2021 and December 31, 2020, respectively.

[2] This entity is a VIE (See Note 2).

[3] On March 30, 2021, the Company sold its interest in the joint venture to the partner. See below for additional details.

[4] The Company’s ownership includes (1) a 33.0% direct interest in the joint venture, and (2) an additional 1% interest in each of the two entities (each, a “Safeco Partner Entity”) through which each partner owns its interest in the joint venture.

[5] The Company’s ownership includes (1) a 35.79% direct interest in the joint venture, (2) an additional 5.837% indirect ownership in the joint venture, and (3) an additional 1% interest in each of the two entities (each, a “360 Park Avenue South Partner Entity”) through which each partner owns its interest in the joint venture.

[6] During the year ended December 31, 2020, the Company recognized an other-than-temporary impairment loss on its investment in the unconsolidated joint venture that owns Dock 72 in Brooklyn, New York totaling approximately $60.5 million.

[7] During the year ended December 31, 2021, the Company completed the sale of its 50% ownership interest in Annapolis Junction NFM LLC. The Company recognized a gain on sale of investment of approximately $10.3 million.