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Investments in Unconsolidated Joint Ventures (Investments in Unconsolidated Joint Ventures) (Details) $ in Thousands | 9 Months Ended |  |  |
--- | --- | --- | --- | ---
Sep. 30, 2017 USD ($) ft² Land_Parcels Buildings payments | Sep. 06, 2017 | Aug. 07, 2017 | Dec. 31, 2016 USD ($)
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Carrying Value of investment |  | $ (419,215) |  |  |  | $ (450,821)
Carrying value of the Company's investments in unconsolidated joint ventures |  | $ 611,800 |  |  |  | 775,198
Square 407 Limited Partnership [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Properties |  | Market Square North |  |  |  |
Ownership Percentage |  | 50.00% |  |  |  |
Carrying Value of investment | [1] | $ (8,474) |  |  |  | (8,134)
The Metropolitan Square Associates LLC [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Properties |  | Metropolitan Square |  |  |  |
Ownership Percentage |  | 20.00% |  |  |  |
Carrying value of the Company's investments in unconsolidated joint ventures | [1] | $ 2,537 |  |  |  | 2,004
BP/CRF 901 New York Avenue LLC [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Properties |  | 901 New York Avenue |  |  |  |
Ownership Percentage | [2] | 25.00% |  |  |  |
Carrying Value of investment | [1] | $ (10,747) |  |  |  | (10,564)
WP Project Developer LLC [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Properties |  | Wisconsin Place Land and Infrastructure |  |  |  |
Ownership Percentage | [3] | 33.30% |  |  |  |
Carrying value of the Company's investments in unconsolidated joint ventures | [1] | $ 40,158 |  |  |  | 41,605
Entity Owning Land And Infrastructure Of Project [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Ownership Percentage |  | 33.30% |  |  |  |
Annapolis Junction NFM, LLC [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Properties |  | Annapolis Junction |  |  |  |
Ownership Percentage | [4] | 50.00% |  |  |  |
Carrying value of the Company's investments in unconsolidated joint ventures | [1] | $ 18,771 |  |  |  | 20,539
Number of real estate properties | Buildings |  | 4 |  |  |  |
Parcels of undeveloped land | Land_Parcels |  | 2 |  |  |  |
540 Madison Venture LLC [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Properties |  | 540 Madison Avenue |  |  |  |
Ownership Percentage |  | 60.00% |  |  |  |
Carrying value of the Company's investments in unconsolidated joint ventures | [1] | $ 67,046 |  |  |  | 67,816
500 North Capitol Venture LLC [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Properties |  | 500 North Capitol Street, NW |  |  |  |
Ownership Percentage |  | 30.00% |  |  |  |
Carrying Value of investment | [1] | $ (3,642) |  |  |  | (3,389)
501 K Street LLC [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Properties |  | 1001 6th Street |  |  |  |
Ownership Percentage | [5] | 50.00% |  |  |  |
Carrying value of the Company's investments in unconsolidated joint ventures | [1] | $ 42,442 |  |  |  | 42,528
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 |  |  |  |
Ownership Percentage |  | 50.00% |  | 50.00% |  |
Carrying value of the Company's investments in unconsolidated joint ventures | [1] | $ 55,917 |  |  |  | 29,869
Residential Tower Developer LLC [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Properties |  | The Hub on Causeway - Residential |  |  |  |
Ownership Percentage |  | 50.00% |  |  |  |
Carrying value of the Company's investments in unconsolidated joint ventures | [1] | $ 25,811 |  |  |  | 20,803
Hotel Tower Developer LLC [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Properties |  | The Hub on Causeway - Hotel |  |  |  |
Ownership Percentage |  | 50.00% |  |  |  |
Carrying value of the Company's investments in unconsolidated joint ventures | [1] | $ 1,596 |  |  |  | 933
1265 Main Office JV LLC [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Properties |  | 1265 Main Street |  |  |  |
Ownership Percentage |  | 50.00% |  |  |  |
Carrying value of the Company's investments in unconsolidated joint ventures | [1] | $ 4,686 |  |  |  | 4,779
BNY Tower Holdings LLC [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Properties |  | Dock 72 at the Brooklyn Navy Yard |  |  |  |
Ownership Percentage | [6] | 50.00% |  |  |  |
Carrying value of the Company's investments in unconsolidated joint ventures | [1] | $ 67,901 |  |  |  | 33,699
CA-Colorado Center Limited Partnership [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Properties |  | Colorado Center |  |  |  |
Ownership Percentage |  | 50.00% |  |  |  |
Carrying value of the Company's investments in unconsolidated joint ventures | [1] | $ 263,834 |  |  |  | 510,623
7750 Wisconsin Avenue [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Properties |  | 7750 Wisconsin Avenue |  |  |  |
Ownership Percentage |  | 50.00% | [6] |  | 50.00% |
Carrying value of the Company's investments in unconsolidated joint ventures | [1] | $ 21,101 |  |  |  |
Unconsolidated Joint Ventures [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Carrying value of the Company's investments in unconsolidated joint ventures |  | (22,900) |  |  |  | (22,100)
Unconsolidated Joint Ventures [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Carrying Value of investment |  | (86,971) |  |  |  | (67,167)
Carrying value of the Company's investments in unconsolidated joint ventures | [1],[7] | $ 588,937 |  |  |  | $ 753,111
[1] | Investments with deficit balances aggregating approximately $22.9 million and $22.1 million at September 30, 2017 and December 31, 2016, respectively, have been reflected 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.
[3] | The Company’s wholly-owned entity that owns the office component of the project also owns a 33.3% interest in the entity owning the land, parking garage and infrastructure of the project.
[4] | The joint venture owns four in-service buildings and two undeveloped land parcels.
[5] | 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.
[6] | The entity is a VIE (See Note 2).
[7] | Investments with deficit balances aggregating approximately $22.9 million and $22.1 million at September 30, 2017 and December 31, 2016, respectively, have been reflected within Other Liabilities in the Company’s Consolidated Balance Sheets.

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