Investments in Unconsolidated Joint Ventures (Investments in Unconsolidated Joint Ventures) (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2023	Dec. 31, 2022
Schedule of Equity Method Investments [Line Items]
Other Liabilities		$ (380,014)	$ (450,918)
Investments in unconsolidated joint ventures		1,536,822	1,715,911
Investments In Affiliates Subsidiaries Associates And Joint Ventures net	[1]	1,496,848	1,630,485
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Other Liabilities		$ (40,000)	(85,400)
Square 407 Limited Partnership [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Market Square North
Ownership Percentage		50.00%
Other Liabilities	[1]	$ (6,020)	(6,198)
BP/CRF Metropolitan Square LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Metropolitan Square
Ownership Percentage	[2]	20.00%
Other Liabilities	[1]	$ 0	(37,629)
901 New York Avenue LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		901 New York Avenue
Ownership Percentage	[3]	25.00%
Other Liabilities	[1]	$ (11,944)	$ (12,493)
901 New York Avenue LLC (economic ownership) [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		50.00%	50.00%
WP Project Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Wisconsin Place Land and Infrastructure
Ownership Percentage	[4]	33.33%
Investments in unconsolidated joint ventures	[1]	$ 30,890	$ 31,971
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]	$ (9,815)	(9,185)
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]	$ 44,506	42,922
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]	$ 46,811	46,839
Residential Tower Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Hub50House
Ownership Percentage		50.00%
Investments in unconsolidated joint ventures	[1]	$ 45,413	45,414
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]	$ 12,033	12,366
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]	$ 58,174	59,716
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]	$ 3,564	3,465
BNY Tower Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Dock 72
Ownership Percentage	[5]	50.00%
Other Liabilities	[1]	$ (12,195)	(19,921)
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]	$ 237,286	233,862
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]	$ 50,442	52,152
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]	$ 115,142	116,397
SMBP Venture LP [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Santa Monica Business Park
Ownership Percentage		55.00%
Investments in unconsolidated joint ventures	[1]	$ 158,561	164,735
Platform 16 Holdings LP [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Platform 16
Ownership Percentage	[6],[7]	55.00%
Investments in unconsolidated joint ventures	[1]	$ 35,719	158,109
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]	$ 362,995	324,038
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]	$ 27,021	27,000
Safeco Plaza REIT LLC
Schedule of Equity Method Investments [Line Items]
Properties		Safeco Plaza
Ownership Percentage	[7],[8]	33.67%
Investments in unconsolidated joint ventures	[1]	$ 42,330	69,785
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	[7],[9]	42.21%
Investments in unconsolidated joint ventures	[1]	$ 59,979	114,992
360 PAS Holdco LLC | Company's Share [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		35.79%
360 PAS Holdco LLC | Joint Venture Partner [Member] | Scenario, Plan
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		58.00%
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]	$ 14,551	11,351
751 Gateway Holdings LLC
Schedule of Equity Method Investments [Line Items]
Properties		751 Gateway
Ownership Percentage		49.00%
Investments in unconsolidated joint ventures	[1]	$ 90,733	80,714
200 Fifth Avenue JV LLC
Schedule of Equity Method Investments [Line Items]
Properties		200 Fifth Avenue
Ownership Percentage	[7]	26.69%
Investments in unconsolidated joint ventures	[1]	$ 83,244	$ 120,083
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]	$ 17,428
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 Park Avenue South Partners Entity Two | 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		5.837%

[1] Investments with deficit balances aggregating approximately $40.0 million and $85.4 million at September 30, 2023 and December 31, 2022, respectively, are included within Other Liabilities in the Company’s Consolidated Balance Sheets.

[2] This entity is a VIE as of September 30, 2023 (See Note 2). During the three months ended September 30, 2023, the Company completed a restructuring of its ownership in Metropolitan Square, as described below in this Note 5 and Note 14.

[3] The Company’s economic ownership has increased based on the achievement of certain return thresholds. At September 30, 2023 and December 31, 2022, the Company’s economic ownership was approximately 50%.

[4] 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.

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

[6] At December 31, 2022, this entity was a VIE.

[7] During the three months ended September 30, 2023, the Company recognized an other-than-temporary impairment loss on its investment.

[8] 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.

[9] The Company’s ownership includes (1) a 35.79% direct interest in the joint venture, (2) an additional 5.837% indirect ownership in the joint venture, and (3) an additional 1% interest in each of the two entities through which each partner owns its interest in the joint venture. The Company’s partners will fund required capital until their aggregate investment is approximately 58% of all capital contributions; thereafter, the partners will fund required capital according to their percentage interests.