Investments in Unconsolidated Joint Ventures (Investments in Unconsolidated Joint Ventures) (Details) $ in Thousands		6 Months Ended
		Jun. 30, 2021 USD ($) ft² payments		Jun. 11, 2021	Mar. 30, 2021	Feb. 25, 2021	Dec. 31, 2020 USD ($)
Schedule of Equity Method Investments [Line Items]
Other Liabilities		$ (370,990)					$ (412,084)
Investments in unconsolidated joint ventures		1,305,589					1,310,478
Investments In Affiliates Subsidiaries Associates And Joint Ventures net	[1]	1,270,102					1,273,919
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Other Liabilities		$ (35,500)					(36,600)
Square 407 Limited Partnership [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Market Square North
Ownership Percentage		50.00%
Other Liabilities	[1]	$ (2,606)					(3,766)
BP/CRF Metropolitan Square LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Metropolitan Square
Ownership Percentage		20.00%
Other Liabilities	[1]	$ (13,223)					(13,584)
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]	$ (12,191)					$ (12,264)
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	[3]	33.30%
Investments in unconsolidated joint ventures	[1]	$ 34,505					$ 35,297
Annapolis Junction NFM, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Annapolis Junction
Ownership Percentage					50.00%		50.00%	[4]
Investments in unconsolidated joint ventures	[1]						$ 13,463
540 Madison Venture
Schedule of Equity Method Investments [Line Items]
Properties		540 Madison Avenue
Ownership Percentage	[5]	60.00%
Investments in unconsolidated joint ventures	[1]						122
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]	$ (7,467)					(6,945)
501 K Street LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		1001 6th Street
Ownership Percentage	[6]	50.00%
Investments in unconsolidated joint ventures	[1]	$ 42,495					42,499
Potential additonal payments to joint venture partner | payments		2
Minimum square footage to make a potential additional payment to joint venture partner (in sqft) | ft²		520,000
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]	$ 49,006					48,818
Residential Tower Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Hub50House
Ownership Percentage		50.00%
Investments in unconsolidated joint ventures	[1]	$ 48,520					50,943
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]	$ 11,316					10,754
Office Tower Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		100 Causeway Street
Ownership Percentage		50.00%		50.00%
Investments in unconsolidated joint ventures	[1]	$ 56,589					56,312
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]	$ 3,757					3,787
BNY Tower Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Dock 72
Ownership Percentage		50.00%
Investments in unconsolidated joint ventures	[1]	$ 28,116					29,536
BNYA Amenity Operator LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Dock 72
Ownership Percentage		50.00%
Investments in unconsolidated joint ventures	[1]	$ 1,297					1,846
CA-Colorado Center Limited Partnership [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Colorado Center
Ownership Percentage		50.00%
Investments in unconsolidated joint ventures	[1]	$ 229,564					227,671
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]	$ 59,208					58,112
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]	$ 116,848					113,774
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]	$ 157,593					145,761
Platform 16 Holdings LP [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Platform 16
Ownership Percentage	[7]	55.00%
Investments in unconsolidated joint ventures	[1]	$ 108,241					$ 108,393
Gateway Portfolio Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Gateway Commons
Ownership Percentage		50.00%	[8]			54.00%	55.00%
Investments in unconsolidated joint ventures	[1]	$ 331,389					$ 336,206
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]	$ 27,145					$ 27,184
Entity Owning Land And Infrastructure Of Project [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		33.30%
Gateway Commons Complex prior to deferred contribution [Member] [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		53.00%					55.00%
Gateway Commons Complex Future Development[Member] [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		49.00%
Joint Venture Partner [Member] | Gateway Commons Complex Future Development[Member] [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		51.00%

[1] Investments with deficit balances aggregating approximately $35.5 million and $36.6 million at June 30, 2021 and December 31, 2020, respectively, are included within Other Liabilities in the Company’s Consolidated Balance Sheets.

[2] The Company’s economic ownership has increased based on the achievement of certain return thresholds. At June 30, 2021 and December 31, 2020, the Company’s economic ownership was approximately 50%.

[3] The Company’s wholly-owned subsidiary that owns Wisconsin Place Office also owns a 33.3% interest in the joint venture entity that owns the land, parking garage and infrastructure of the project.

[4] On March 30, 2021, the Company sold its interest in the joint venture to the partner. See below for additional details.

[5] The property was sold on June 27, 2019. As of December 31, 2020, the investment consisted of undistributed cash. All remaining cash has been distributed as of June 30, 2021.

[6] Under the joint venture agreement for this land parcel, the partner will be entitled to up to two additional payments from the venture based on increases in total entitled square footage of the project above 520,000 square feet and achieving certain project returns at stabilization.

[7] This entity is a VIE (See Note 2).

[8] As a result of the partner’s deferred contribution, the Company owned an approximately 53% and 55% interest in the joint venture at June 30, 2021 and December 31, 2020, respectively. Future development projects will be owned 49% by the Company and 51% by its partner.