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Real Estate (Narrative) (Details) $ in Thousands				12 Months Ended
		Dec. 27, 2024 USD ($) ft²	Jan. 08, 2024 USD ($) ft²	Dec. 31, 2024 USD ($) ft² Real_Estate_Properties	Dec. 31, 2024 USD ($) ft² Real_Estate_Properties	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 20, 2024 USD ($)	Oct. 31, 2024 ft²	Oct. 05, 2024 ft²	Sep. 26, 2024 ft²	Jul. 22, 2024 USD ($)	Jul. 17, 2024 ft²	May 07, 2024 USD ($) ft²	Apr. 05, 2024 ft²	Feb. 12, 2024 ft² apartments	Jan. 07, 2024 USD ($)
Real Estate Properties [Line Items]
Total revenue				$ 3,407,719		$ 3,273,569	$ 3,108,581
Net Income (Loss)				14,272		190,215	848,947
Carying value of the Company's investment in unconsolidated joint ventures				1,093,583	$ 1,093,583	1,377,319
Impairment loss				$ 13,615		$ 0	$ 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				2,300,000	2,300,000
Number of real estate properties | Real_Estate_Properties				7	7
901 New York Avenue
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²			508,000
Payments to Acquire Investments			$ 10,000
Net Working Capital, Including Cash Acquired from Acquisition			7,100
Gain on sale / consolidation			21,800
Total revenue					$ 33,200
Net Income (Loss)					$ (9,400)
Asset Acquisition, Consideration Transferred			20,000
901 New York Avenue | Unconsolidated Properties
Real Estate Properties [Line Items]
Gain 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					$ 202,300
Assumption of mortgage notes payable			$ 207,100
901 New York Avenue | Joint Venture Partner [Member] | 901 New York Avenue LLC [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%
725 12th Street
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²		300,000
Number of floors		12
Payments to Acquire Buildings		$ 34,000
725 12th Street | Construction in Progress
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²		320,000
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
760 Boylston Street
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²															118,000
Reston Next Office Phase II
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²													90,000
180 CityPoint [Member]
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²											329,000
103 CityPoint
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²										113,000
300 Binney Street
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²									240,000
Shady Grove Innovation District [Member]
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²														143,000
Impairment loss				$ 13,600
Number of real estate properties														2
Contractual Sales Price												$ 24,700		$ 24,800
[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 6. Since then, the Company accounts for its assets, liabilities and operations on a consolidated basis.

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