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Investments in Unconsolidated Joint Ventures (Investments in Unconsolidated Joint Ventures) (Details) - USD ($) $ in Thousands |  |  | 7 Months Ended | 9 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Jun. 27, 2025 | Mar. 05, 2025 | Sep. 30, 2025 | Sep. 30, 2025 | Sep. 30, 2024 | Sep. 17, 2025 | Aug. 20, 2025 | Aug. 07, 2025 | Feb. 27, 2025 | Dec. 31, 2024
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Other Liabilities |  |  |  | $ (406,820) |  | $ (406,820) |  |  |  |  |  |  | $ (450,796)
Investments in unconsolidated joint ventures |  |  |  | 999,764 |  | 999,764 |  |  |  |  |  |  | 1,093,583
Investments In Affiliates Subsidiaries Associates And Joint Ventures net | [1] |  |  | 949,312 |  | 949,312 |  |  |  |  |  |  | 1,060,074
Payments to Acquire Equity Method Investments |  |  |  |  |  | 118,524 |  | $ 87,498 |  |  |  |  |
Unconsolidated Joint Ventures [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Other Liabilities |  |  |  | $ (50,500) |  | $ (50,500) |  |  |  |  |  |  | (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] |  |  | $ (23,691) |  | $ (23,691) |  |  |  |  |  |  | (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] |  |  | $ 29,209 |  | $ 29,209 |  |  |  |  |  |  | 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] |  |  | $ (12,435) |  | $ (12,435) |  |  |  |  |  |  | (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] |  |  | $ 45,772 |  | $ 45,772 |  |  |  |  |  |  | 45,903
Podium Venture LLC [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | The Hub on Causeway - Podium |  |  |  |  |  |  |
Ownership Percentage |  |  |  | 50.00% | [3] | 50.00% | [3] |  |  | 50.00% |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 55,231 |  | $ 55,231 |  |  |  |  |  |  | 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] |  |  | $ 33,654 |  | $ 33,654 |  |  |  |  |  |  | 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] |  |  | $ 11,849 |  | $ 11,849 |  |  |  |  |  |  | 14,271
Office Venture LLC |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | 100 Causeway Street |  |  |  |  |  |  |
Ownership Percentage |  |  |  | 50.00% | [3] | 50.00% | [3] |  |  | 50.00% |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 48,833 |  | $ 48,833 |  |  |  |  |  |  | 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] |  |  | $ 3,217 |  | $ 3,217 |  |  |  |  |  |  | 3,476
BNY Tower Holdings LLC [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | Dock 72 |  |  |  |  |  |  |
Ownership Percentage | [4] |  |  | 50.00% |  | 50.00% |  |  |  |  |  |  |
Other Liabilities | [1] |  |  | $ (14,326) |  | $ (14,326) |  |  |  |  |  |  | (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] |  |  | $ 69,015 |  | $ 69,015 |  |  |  |  |  |  | 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] |  |  | $ 47,363 |  | $ 47,363 |  |  |  |  |  |  | 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] |  |  | $ 110,581 |  | $ 110,581 |  |  |  |  |  |  | 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] |  |  | $ 58,076 |  | $ 58,076 |  |  |  |  |  |  | 56,265
Gateway Portfolio Holdings LLC [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | Gateway Commons |  |  |  |  |  |  |
Ownership Percentage | [5] |  |  | 50.00% |  | 50.00% |  |  |  |  |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 125,090 |  | $ 125,090 |  |  |  |  |  |  | 272,000
Rosecrans-Sepulveda Partners 4, LLC |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | Beach Cities Media Campus |  |  |  |  |  |  |
Ownership Percentage |  |  |  | 50.00% | [6] | 50.00% | [6] |  | 50.00% |  |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 98 |  | $ 98 |  |  |  |  |  |  | 27,051
Safeco Plaza REIT LLC |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Properties |  |  |  |  |  | Safeco Plaza |  |  |  |  |  |  |
Ownership Percentage | [7] |  |  | 33.67% |  | 33.67% |  |  |  |  |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 121 |  | $ 121 |  |  |  |  |  |  | 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 |  |  |  | 71.11% | [8] | 71.11% | [8] |  |  |  | 71.11% |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 93,988 |  | $ 93,988 |  |  |  |  |  |  | 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] |  |  | $ 14,702 |  | $ 14,702 |  |  |  |  |  |  | 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] |  |  | $ 118,509 |  | $ 118,509 |  |  |  |  |  |  | 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] |  |  | $ 75,376 |  | $ 75,376 |  |  |  |  |  |  | 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] |  |  | $ 19,855 |  | $ 19,855 |  |  |  |  |  |  | $ 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% | [9] | 19.46% | [9] |  |  |  |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 19,813 |  | $ 19,813 |  |  |  |  |  |  |
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 | [9],[10] |  |  | 0.00% |  | 0.00% |  |  |  |  |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 12,014 |  | $ 12,014 |  |  |  |  |  |  |
Payments to Acquire Equity Method Investments |  |  |  | $ 11,900 |  |  |  |  |  |  |  |  |
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% | [9] | 20.00% | [9] |  |  |  |  |  |
Investments in unconsolidated joint ventures | [1] |  |  | $ 7,398 |  | $ 7,398 |  |  |  |  |  |  |
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 $50.5 million and $33.5 million at September 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] | In conjunction with the execution of the mortgage loan signed on September 30, 2025 (described below), Podium Venture LLC and Office Venture LLC were created for structuring purposes and did not change any of the partner rights previously held by the partners of Podium Developer LLC or Office Tower Developer LLC, respectively.
[4] | This investment includes net equity balances from the amenity joint venture.
[5] | During the three months ended September 30, 2025, the Company recognized an other-than-temporary impairment loss on its investment.
[6] | On September 17, 2025, the joint venture completed the sale of Beach Cities Media Campus, a land parcel, located in El Segundo, California.
[7] | 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.
[8] | 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.
[9] | This entity is a VIE (See Note 2).
[10] | 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 and accrue 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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