Investment in Unconsolidated Joint Ventures (Narrative) (Details) $ in Thousands						3 Months Ended
		Feb. 09, 2024 USD ($) ft²	Feb. 06, 2024 USD ($)	Jan. 11, 2024	Jan. 08, 2024 USD ($) ft²	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)	Jan. 07, 2024	Jan. 02, 2024 ft²
Schedule of Equity Method Investments [Line Items]
Interest and Other Income						$ 14,529	$ 10,941
3 Hudson Boulevard [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage						25.00%
901 New York Avenue LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage	[1]					25.00%
Gateway Commons Complex [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage						50.00%
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Gain (loss) on sale / consolidation						$ 21,696	$ 0
Unconsolidated Properties | 651 Gateway | Office and Life Sciences Building [Member]
Schedule of Equity Method Investments [Line Items]
Net Rentable Area (in sf) | ft²									327,000
Leased percentage									21.00%
Unconsolidated Properties | Gateway Commons Complex [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage									50.00%
3 Hudson Boulevard [Member] | Extended Maturity
Schedule of Equity Method Investments [Line Items]
Debt Instrument, Maturity Date			May 09, 2024
3 Hudson Boulevard [Member] | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Ownership Percentage			25.00%
Debt			$ 80,000
3 Hudson Boulevard [Member] | Unconsolidated Properties | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Schedule of Equity Method Investments [Line Items]
Debt Instrument, Basis Spread on Variable Rate			3.61%
7750 Wisconsin Avenue [Member] | Extended Maturity
Schedule of Equity Method Investments [Line Items]
Debt Instrument, Maturity Date		Apr. 26, 2025
7750 Wisconsin Avenue [Member] | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		50.00%
Net Rentable Area (in sf) | ft²		736,000
Construction Loan		$ 252,600
Long-Term Debt		$ 251,600
7750 Wisconsin Avenue [Member] | Unconsolidated Properties | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Schedule of Equity Method Investments [Line Items]
Debt Instrument, Basis Spread on Variable Rate		1.35%
901 New York Avenue
Schedule of Equity Method Investments [Line Items]
Net Rentable Area (in sf) | ft²					524,000
Payments to Acquire Investments					$ 10,000
Gain (loss) on sale / consolidation					$ 21,800
901 New York Avenue | Joint Venture Partner [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage					50.00%
901 New York Avenue | Mortgages [Member]
Schedule of Equity Method Investments [Line Items]
Debt					$ 207,100
Number of extensions				2
Debt Instrument, Interest Rate, Stated Percentage					3.61%
Debt Instrument, Maturity Date					Jan. 05, 2025
901 New York Avenue | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Gain (loss) on sale / consolidation					$ 21,800
901 New York Avenue | Unconsolidated Properties | 901 New York Avenue LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage								50.00%
901 New York Avenue | Unconsolidated Properties | 901 New York Avenue LLC [Member] | Joint Venture Partner [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage					50.00%

[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.