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Investments in Unconsolidated Joint Ventures (Investments in Unconsolidated Joint Ventures) (Details) - USD ($) $ in Thousands |  |  | 4 Months Ended | 6 Months Ended |  |
--- | --- | --- | --- | --- | --- | ---
Jun. 27, 2025 | Mar. 05, 2025 | Jun. 30, 2025 | Jun. 30, 2025 | Jun. 30, 2024 | Feb. 27, 2025 | Dec. 31, 2024
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Other Liabilities |  |  |  | $ (416,838) |  | $ (416,838) |  |  |  | $ (450,796)
Investments in unconsolidated joint ventures |  |  |  | 1,161,036 |  | 1,161,036 |  |  |  | 1,093,583
Investments In Affiliates Subsidiaries Associates And Joint Ventures net | [1] |  |  | 1,112,904 |  | 1,112,904 |  |  |  | 1,060,074
Payments to Acquire Equity Method Investments |  |  |  |  |  | 84,432 |  | $ 60,461 |  |
Unconsolidated Joint Ventures [Member] |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Other Liabilities |  |  |  | $ (48,100) |  | $ (48,100) |  |  |  | (33,500)
Square 407 Limited Partnership [Member] |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | Market Square North |  |  |  |
Ownership Percentage |  |  |  | 50.00% |  | 50.00% |  |  |  |
Other Liabilities | [1] |  |  | $ (23,685) |  | $ (23,685) |  |  |  | (11,924)
WP Project Developer LLC [Member] |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | Wisconsin Place Land and Infrastructure |  |  |  |
Ownership Percentage | [2] |  |  | 33.33% |  | 33.33% |  |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 29,534 |  | $ 29,534 |  |  |  | 29,775
500 North Capitol Venture LLC [Member] |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | 500 North Capitol Street, NW |  |  |  |
Ownership Percentage |  |  |  | 30.00% |  | 30.00% |  |  |  |
Other Liabilities | [1] |  |  | $ (12,486) |  | $ (12,486) |  |  |  | (11,696)
501 K Street LLC [Member] |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | 1001 6th Street |  |  |  |
Ownership Percentage |  |  |  | 50.00% |  | 50.00% |  |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 45,837 |  | $ 45,837 |  |  |  | 45,903
Podium Developer LLC [Member] |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | The Hub on Causeway - Podium |  |  |  |
Ownership Percentage |  |  |  | 50.00% |  | 50.00% |  |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 40,492 |  | $ 40,492 |  |  |  | 42,310
Residential Tower Developer LLC [Member] |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | Hub50House |  |  |  |
Ownership Percentage |  |  |  | 50.00% |  | 50.00% |  |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 39,498 |  | $ 39,498 |  |  |  | 42,493
Hotel Tower Developer LLC [Member] |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | The Hub on Causeway - Hotel Air Rights |  |  |  |
Ownership Percentage |  |  |  | 50.00% |  | 50.00% |  |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 14,662 |  | $ 14,662 |  |  |  | 14,271
Office Tower Developer LLC |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | 100 Causeway Street |  |  |  |
Ownership Percentage |  |  |  | 50.00% |  | 50.00% |  |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 55,852 |  | $ 55,852 |  |  |  | 55,810
1265 Main Office JV LLC [Member] |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | 1265 Main Street |  |  |  |
Ownership Percentage |  |  |  | 50.00% |  | 50.00% |  |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 3,340 |  | $ 3,340 |  |  |  | 3,476
BNY Tower Holdings LLC [Member] |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | Dock 72 |  |  |  |
Ownership Percentage | [3] |  |  | 50.00% |  | 50.00% |  |  |  |
Other Liabilities | [1] |  |  | $ (11,961) |  | $ (11,961) |  |  |  | (9,889)
CA-Colorado Center LLC[Member] |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | Colorado Center |  |  |  |
Ownership Percentage |  |  |  | 50.00% |  | 50.00% |  |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 70,222 |  | $ 70,222 |  |  |  | 65,000
7750 Wisconsin Avenue LLC [Member] |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | 7750 Wisconsin Avenue |  |  |  |
Ownership Percentage |  |  |  | 50.00% |  | 50.00% |  |  | 50.00% |
Investments in unconsolidated joint ventures | [1] |  |  | $ 48,072 |  | $ 48,072 |  |  |  | 48,423
BP-M 3HB Venture LLC [Member] |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | 3 Hudson Boulevard |  |  |  |
Ownership Percentage |  |  |  | 25.00% |  | 25.00% |  |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 111,471 |  | $ 111,471 |  |  |  | 112,771
Platform 16 Holdings LP [Member] |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | Platform 16 |  |  |  |
Ownership Percentage |  |  |  | 55.00% |  | 55.00% |  |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 57,805 |  | $ 57,805 |  |  |  | 56,265
Gateway Portfolio Holdings LLC [Member] |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | Gateway Commons |  |  |  |
Ownership Percentage |  |  |  | 50.00% |  | 50.00% |  |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 271,454 |  | $ 271,454 |  |  |  | 272,000
Rosecrans-Sepulveda Partners 4, LLC |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | Beach Cities Media Campus |  |  |  |
Ownership Percentage |  |  |  | 50.00% |  | 50.00% |  |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 27,068 |  | $ 27,068 |  |  |  | 27,051
Safeco Plaza REIT LLC |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | Safeco Plaza |  |  |  |
Ownership Percentage | [4] |  |  | 33.67% |  | 33.67% |  |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 43 |  | $ 43 |  |  |  | 0
Safeco Plaza REIT LLC | Company's Share [Member] |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Ownership Percentage |  |  |  | 33.00% |  | 33.00% |  |  |  |
360 PAS Holdco LLC |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | 360 Park Avenue South |  |  |  |
Ownership Percentage | [5] |  |  | 71.11% |  | 71.11% |  |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 89,769 |  | $ 89,769 |  |  |  | 74,592
360 PAS Holdco LLC | Company's Share [Member] |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Ownership Percentage |  |  |  | 35.79% |  | 35.79% |  |  |  |
PR II BXP Reston Gateway LLC |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | Skymark - Reston Next Residential |  |  |  |
Ownership Percentage |  |  |  | 20.00% |  | 20.00% |  |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 14,900 |  | $ 14,900 |  |  |  | 14,844
751 Gateway Holdings LLC |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | 751 Gateway |  |  |  |
Ownership Percentage |  |  |  | 49.00% |  | 49.00% |  |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 119,634 |  | $ 119,634 |  |  |  | 99,701
200 Fifth Avenue JV LLC |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | 200 Fifth Avenue |  |  |  |
Ownership Percentage |  |  |  | 26.69% |  | 26.69% |  |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 74,446 |  | $ 74,446 |  |  |  | 70,673
ABXP Worldgate Investments LLC |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | 13100 and 13150 Worldgate Drive |  |  |  |
Ownership Percentage |  |  |  | 50.00% |  | 50.00% |  |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 19,632 |  | $ 19,632 |  |  |  | $ 18,225
Entity Owning Land And Infrastructure Of Project [Member] |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Ownership Percentage |  |  |  | 33.33% |  | 33.33% |  |  |  |
Safeco Partner Entity One [Member] | Company's Share [Member] |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Ownership Percentage |  |  |  | 1.00% |  | 1.00% |  |  |  |
Safeco Partner Entity Two | Company's Share [Member] |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Ownership Percentage |  |  |  | 1.00% |  | 1.00% |  |  |  |
360 Park Avenue South Partners Entity | Company's Share [Member] |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Ownership Percentage |  |  |  | 1.00% |  | 1.00% |  |  |  |
360 PAS Holdco LLC (indirect ownership) | Company's Share [Member] |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Ownership Percentage |  |  |  | 35.02% |  | 35.02% |  |  |  |
CAB 290 Coles Venture LLC |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | 290 Coles Street - Common Equity |  |  |  |
Ownership Percentage |  |  | 19.46% | 19.46% | [6] | 19.46% | [6] |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 19,625 |  | $ 19,625 |  |  |  |
Payments to Acquire Equity Method Investments |  |  | $ 20,000 |  |  |  |  |  |  |
CAB 290 Coles Holdco LLC |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | 290 Coles Street - Preferred Equity |  |  |  |
Ownership Percentage | [6],[7] |  |  | 0.00% |  | 0.00% |  |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 1,615 |  | $ 1,615 |  |  |  |
Payments to Acquire Equity Method Investments |  |  |  | $ 1,600 |  |  |  |  |  |
CAB 290 Coles Holdco LLC | Maximum [Member] |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Payments to Acquire Equity Method Investments |  |  |  |  |  | $ 65,000 |  |  |  |
Internal Rate of return on preferred equity |  |  |  |  |  | 13.00% |  |  |  |
17 Hartwell Avenue JV LLC |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | 17 Hartwell Avenue |  |  |  |
Ownership Percentage |  | 20.00% |  | 20.00% | [6] | 20.00% | [6] |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 6,065 |  | $ 6,065 |  |  |  |
17 Hartwell Avenue JV LLC | Joint Venture Partner [Member] |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Payments to Acquire Equity Method Investments |  | $ 23,000 |  |  |  |  |  |  |  |
[1] | Investments with deficit balances aggregating approximately $48.1 million and $33.5 million at June 30, 2025 and December 31, 2024, respectively, are included within Other Liabilities in the Company’s Consolidated Balance Sheets.
[2] | The Company’s wholly-owned subsidiary that owns Wisconsin Place Office also owns a 33.33% interest in the joint venture entity that owns the land, parking garage and infrastructure of the project.
[3] | This property includes net equity balances from the amenity joint venture.
[4] | The Company’s ownership includes (1) a 33.0% direct interest in the joint venture, and (2) an additional 1.0% interest in each of the two entities 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 35.02% indirect ownership in the joint venture, and (3) an additional 1.0% interest in the entity through which the partner owns its interest in the joint venture.
[6] | This entity is a VIE (See Note 2).
[7] | The Company agreed to fund up to $65.0 million of the required capital through its preferred equity investment. The Company’s preferred equity investment will earn a 13.0% internal rate of return (“IRR”) and is to be redeemed, in full, upon the earlier of two years after stabilization of the property or March 5, 2030.

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