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Investments in Unconsolidated Joint Ventures (Investments in Unconsolidated Joint Ventures) (Details) $ in Thousands |  | 9 Months Ended |  |
--- | --- | --- | --- | ---
Jul. 13, 2018 ft² | Sep. 30, 2018 USD ($) ft² Land_Parcels Buildings payments | Jul. 27, 2018 ft² | Dec. 31, 2017 USD ($)
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Carrying Value of investment |  |  | $ (468,433) |  |  | $ (443,980)
Carrying value of the Company's investments in unconsolidated joint ventures |  |  | $ 925,431 |  |  | 619,925
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] |  | $ (6,870) |  |  | (8,258)
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] |  | $ 1,220 |  |  | 3,339
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] |  | $ (12,454) |  |  | (13,811)
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] |  | $ 38,667 |  |  | 39,710
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] |  | $ 17,309 |  |  | 18,381
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] |  | $ 66,492 |  |  | 66,179
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] |  | $ (4,699) |  |  | (3,876)
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] |  | $ 42,584 |  |  | 42,657
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% |  |  |
Carrying value of the Company's investments in unconsolidated joint ventures | [1] |  | $ 68,919 |  |  | 67,120
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] |  | $ 46,655 |  |  | 28,212
Hotel Tower Developer LLC [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Properties |  |  | The Hub on Causeway - Hotel Air Rights |  |  |
Ownership Percentage |  |  | 50.00% |  |  |
Carrying value of the Company's investments in unconsolidated joint ventures | [1] |  | $ 2,738 |  |  | 1,690
Office Tower Developer LLC [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Properties |  |  | 100 Causeway Street |  |  |
Ownership Percentage |  |  | 50.00% | [6] | 50.00% |
Carrying value of the Company's investments in unconsolidated joint ventures | [1] |  | $ 12,232 |  |  | 0
Net Rentable Area (in sf) | ft² |  |  |  |  | 627,000 |
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] |  | $ 4,313 |  |  | 4,641
BNY Tower Holdings LLC [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Properties |  |  | Dock 72 |  |  |
Ownership Percentage |  |  | 50.00% |  |  |
Carrying value of the Company's investments in unconsolidated joint ventures | [1] |  | $ 72,100 |  |  | 72,104
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] |  | $ 253,334 |  |  | 254,440
7750 Wisconsin Avenue LLC [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Properties |  |  | 7750 Wisconsin Avenue |  |  |
Ownership Percentage | [6] |  | 50.00% |  |  |
Carrying value of the Company's investments in unconsolidated joint ventures | [1] |  | $ 69,007 |  |  | 21,452
BP-M 3HB Venture LLC [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Debt Instrument, Basis Spread on Variable Rate |  | 3.50% |  |  |  |
Properties |  |  | 3 Hudson Boulevard |  |  |
Ownership Percentage |  | 25.00% | 25.00% |  |  |
Carrying value of the Company's investments in unconsolidated joint ventures | [1] |  | $ 46,240 |  |  | 0
Net Rentable Area (in sf) | ft² |  | 2,000,000.0 |  |  |  |
SMBP Venture LP [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Properties |  |  | Santa Monica Business Park |  |  |
Ownership Percentage |  |  | 55.00% |  |  |
Carrying value of the Company's investments in unconsolidated joint ventures | [1] |  | $ 183,621 |  |  | 0
Unconsolidated Joint Ventures [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Carrying Value of investment |  |  | 24,000 |  |  | 25,900
Unconsolidated Joint Ventures [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Carrying Value of investment |  |  | (589,394) |  |  | (99,215)
Carrying value of the Company's investments in unconsolidated joint ventures | [1],[7] |  | $ 901,408 |  |  | $ 593,980
[1] | Investments with deficit balances aggregating approximately $24.0 million and $25.9 million at September 30, 2018 and December 31, 2017, 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 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] | 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] | This entity is a VIE (See Note 2 to the Consolidated Financial Statements).
[7] | Investments with deficit balances aggregating approximately $24.0 million and $25.9 million at September 30, 2018 and December 31, 2017, respectively, have been reflected within Other Liabilities in the Company’s Consolidated Balance Sheet

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