Investments in Unconsolidated Joint Ventures (Investments in Unconsolidated Joint Ventures) (Details) - USD ($) $ in Thousands			3 Months Ended
		Jan. 08, 2024	Mar. 31, 2024	Dec. 31, 2023
Schedule of Equity Method Investments [Line Items]
Other Liabilities			$ (417,978)	$ (445,947)
Investments in unconsolidated joint ventures			1,399,824	1,377,319
Investments In Affiliates Subsidiaries Associates And Joint Ventures net	[1]		1,370,447	1,337,416
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Other Liabilities			$ (29,400)	(39,900)
Square 407 Limited Partnership [Member]
Schedule of Equity Method Investments [Line Items]
Properties			Market Square North
Ownership Percentage			50.00%
Other Liabilities	[1]		$ (6,103)	(5,996)
901 New York Avenue LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties			901 New York Avenue
Ownership Percentage	[2]		25.00%
Other Liabilities	[1]			$ (11,764)
901 New York Avenue LLC (economic ownership) [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage				50.00%
Payments to Acquire Real Estate and Real Estate Joint Ventures		$ 10,000
901 New York Avenue LLC (economic ownership) [Member] | Joint Venture Partner [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		50.00%
WP Project Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties			Wisconsin Place Land and Infrastructure
Ownership Percentage	[3]		33.33%
Investments in unconsolidated joint ventures	[1]		$ 30,221	$ 30,375
500 North Capitol Venture LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties			500 North Capitol Street, NW
Ownership Percentage			30.00%
Other Liabilities	[1]		$ (10,773)	(10,253)
501 K Street LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties			1001 6th Street
Ownership Percentage			50.00%
Investments in unconsolidated joint ventures	[1]		$ 45,013	44,774
Podium Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties			The Hub on Causeway - Podium
Ownership Percentage			50.00%
Investments in unconsolidated joint ventures	[1]		$ 45,068	45,201
Residential Tower Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties			Hub50House
Ownership Percentage			50.00%
Investments in unconsolidated joint ventures	[1]		$ 42,250	40,235
Hotel Tower Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties			The Hub on Causeway - Hotel Air Rights
Ownership Percentage			50.00%
Investments in unconsolidated joint ventures	[1]		$ 13,680	13,494
Office Tower Developer LLC
Schedule of Equity Method Investments [Line Items]
Properties			100 Causeway Street
Ownership Percentage			50.00%
Investments in unconsolidated joint ventures	[1]		$ 57,079	57,660
1265 Main Office JV LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties			1265 Main Street
Ownership Percentage			50.00%
Investments in unconsolidated joint ventures	[1]		$ 3,583	3,585
BNY Tower Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties			Dock 72
Ownership Percentage	[4]		50.00%
Other Liabilities	[1]		$ (12,501)	(11,890)
CA-Colorado Center LLC[Member]
Schedule of Equity Method Investments [Line Items]
Properties			Colorado Center
Ownership Percentage			50.00%
Investments in unconsolidated joint ventures	[1]		$ 235,143	237,815
7750 Wisconsin Avenue LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties			7750 Wisconsin Avenue
Ownership Percentage			50.00%
Investments in unconsolidated joint ventures	[1]		$ 49,756	50,064
BP-M 3HB Venture LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties			3 Hudson Boulevard
Ownership Percentage			25.00%
Investments in unconsolidated joint ventures	[1]		$ 114,331	115,103
Platform 16 Holdings LP [Member]
Schedule of Equity Method Investments [Line Items]
Properties			Platform 16
Ownership Percentage			55.00%
Investments in unconsolidated joint ventures	[1]		$ 51,349	45,564
Gateway Portfolio Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties			Gateway Commons
Ownership Percentage			50.00%
Investments in unconsolidated joint ventures	[1]		$ 385,568	376,834
Rosecrans-Sepulveda Partners 4, LLC
Schedule of Equity Method Investments [Line Items]
Properties			Beach Cities Media Campus
Ownership Percentage			50.00%
Investments in unconsolidated joint ventures	[1]		$ 27,042	27,034
Safeco Plaza REIT LLC
Schedule of Equity Method Investments [Line Items]
Properties			Safeco Plaza
Ownership Percentage	[5]		33.67%
Investments in unconsolidated joint ventures	[1]		$ 43,860	44,734
Safeco Plaza REIT LLC | Company's Share [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage			33.00%
360 PAS Holdco LLC
Schedule of Equity Method Investments [Line Items]
Properties			360 Park Avenue South
Ownership Percentage	[6]		71.11%
Investments in unconsolidated joint ventures	[1]		$ 49,888	42,988
360 PAS Holdco LLC | Company's Share [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage			35.79%
PR II BXP Reston Gateway LLC
Schedule of Equity Method Investments [Line Items]
Properties			Skymark - Reston Next Residential
Ownership Percentage			20.00%
Investments in unconsolidated joint ventures	[1]		$ 15,323	15,184
751 Gateway Holdings LLC
Schedule of Equity Method Investments [Line Items]
Properties			751 Gateway
Ownership Percentage			49.00%
Investments in unconsolidated joint ventures	[1]		$ 95,863	93,411
200 Fifth Avenue JV LLC
Schedule of Equity Method Investments [Line Items]
Properties			200 Fifth Avenue
Ownership Percentage			26.69%
Investments in unconsolidated joint ventures	[1]		$ 76,728	75,718
ABXP Worldgate Investments LLC
Schedule of Equity Method Investments [Line Items]
Properties			13100 and 13150 Worldgate Drive
Ownership Percentage			50.00%
Investments in unconsolidated joint ventures	[1]		$ 18,079	$ 17,546
Entity Owning Land And Infrastructure Of Project [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage			33.33%
Safeco Partner Entity One [Member] | Company's Share [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage			1.00%
Safeco Partner Entity Two | Company's Share [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage			1.00%
360 Park Avenue South Partners Entity | Company's Share [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage			1.00%
360 PAS Holdco LLC (indirect ownership) | Company's Share [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage			35.02%

[1] Investments with deficit balances aggregating approximately $29.4 million and $39.9 million at March 31, 2024 and December 31, 2023, respectively, are included within Other Liabilities in the Company’s Consolidated Balance Sheets.

[2] 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.

[3] 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.

[4] This property includes net equity balances from the amenity joint venture.

[5] The Company’s ownership includes (1) a 33.0% direct interest in the joint venture, and (2) an additional 1% interest in each of the two entities through which each partner owns its interest in the joint venture.

[6] 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% interest in the entity through which the partner owns its interest in the joint venture.