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Real Estate (Narrative) (Details) $ in Thousands				3 Months Ended		6 Months Ended
		Mar. 31, 2024 USD ($)	Jan. 08, 2024 USD ($) ft²	Jun. 30, 2024 USD ($) ft² Real_Estate_Properties	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($) ft² Real_Estate_Properties	Jun. 30, 2024 USD ($) ft² Real_Estate_Properties	Jun. 30, 2023 USD ($)	May 07, 2024 USD ($) ft²	Apr. 05, 2024 ft²	Feb. 12, 2024 ft² apartments	Jan. 07, 2024 USD ($)	Dec. 31, 2023 USD ($)
Real Estate Properties [Line Items]
Total revenue				$ 850,482	$ 817,153		$ 1,689,921	$ 1,620,353
Net Income (Loss)				79,615	104,299		159,498	182,215
Carying value of the Company's investment in unconsolidated joint ventures				1,418,817		$ 1,418,817	1,418,817						$ 1,377,319
Impairment loss				$ 0	$ 0		$ 13,615	$ 0
901 New York Avenue LLC [Member]
Real Estate Properties [Line Items]
Ownership Percentage	[1]												25.00%
Construction in Progress
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²				3,100,000		3,100,000	3,100,000
Number of real estate properties | Real_Estate_Properties				10		10	10
901 New York Avenue
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²			524,000
Payments to Acquire Investments			$ 10,000
Net Working Capital, Including Cash Acquired from Acquisition			7,100
Gain (loss) on sale / consolidation			21,800
Total revenue						$ 16,300
Net Income (Loss)						$ (4,600)
Asset Acquisition, Consideration Transferred			20,000
901 New York Avenue | Unconsolidated Properties
Real Estate Properties [Line Items]
Gain (loss) on sale / consolidation			21,800
901 New York Avenue | 901 New York Avenue LLC [Member]
Real Estate Properties [Line Items]
Carying value of the Company's investment in unconsolidated joint ventures												$ (11,800)
Investments in Affiliates, Subsidiaries, Associates, and Joint Ventures, Fair Value Disclosure			10,000
901 New York Avenue | 901 New York Avenue LLC [Member] | Unconsolidated Properties
Real Estate Properties [Line Items]
Ownership Percentage												50.00%
901 New York Avenue | Mortgages [Member]
Real Estate Properties [Line Items]
Debt			207,100
Assumption of mortgage notes payable			$ 207,100
901 New York Avenue | Joint Venture Partner [Member]
Real Estate Properties [Line Items]
Ownership Percentage			50.00%
901 New York Avenue | Joint Venture Partner [Member] | 901 New York Avenue LLC [Member] | Unconsolidated Properties
Real Estate Properties [Line Items]
Ownership Percentage			50.00%
Shady Grove Innovation District [Member]
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²									143,000
Impairment loss		$ 13,600					$ 13,600
Number of real estate properties									2
Contractual Sales Price									$ 24,800
760 Boylston Street
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²										118,000
121 Broadway | Construction in Progress | Residential Properties [Member]
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²											492,000
Number of Units in Real Estate Property | apartments											439
[1] At December 31, 2023, the Company’s economic ownership was approximately 50%. On January 8, 2024, the Company completed the acquisition of its joint venture partner’s 50% economic ownership interest for a gross purchase price of $10.0 million, as described in Note 3 and this Note 5. Since then, the Company accounts for its assets, liabilities and operations on a consolidated basis.

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