Real Estate (Narrative) (Details) $ in Thousands				3 Months Ended
		Mar. 31, 2024 USD ($) ft² Real_Estate_Properties	Jan. 08, 2024 USD ($) ft²	Mar. 31, 2024 USD ($) ft² Real_Estate_Properties	Mar. 31, 2024 USD ($) ft² Real_Estate_Properties	Mar. 31, 2023 USD ($)	Feb. 12, 2024 ft² apartments	Jan. 07, 2024 USD ($)	Dec. 31, 2023 USD ($)
Real Estate Properties [Line Items]
Total revenue				$ 839,439		$ 803,200
Net Income (Loss)				79,883		77,890
Depreciation and amortization				218,716		208,734
Carying value of the Company's investment in unconsolidated joint ventures		$ 1,399,824		1,399,824	$ 1,399,824				$ 1,377,319
Impairment loss				$ 13,615		$ 0
901 New York Avenue LLC [Member]
Real Estate Properties [Line Items]
Ownership Percentage	[1]	25.00%		25.00%	25.00%
Construction in Progress
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²		3,200,000		3,200,000	3,200,000
Number of real estate properties | Real_Estate_Properties		11		11	11
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
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					$ 7,900
Net Income (Loss)					$ (2,300)
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]
Impairment loss		$ 13,600

[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.