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Real Estate Investments - Summary of Office Properties Sold (Parenthetical) (Details) |  | 3 Months Ended | 12 Months Ended |  |  |  |
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Apr. 03, 2014 USD ($) ft² property Storey | Dec. 31, 2015 USD ($) ft² property Storey | Jun. 30, 2015 USD ($) | Mar. 31, 2015 USD ($) | Sep. 30, 2014 USD ($) | Dec. 31, 2015 USD ($) ft² property Storey | Dec. 31, 2014 USD ($) ft² property | Dec. 31, 2013 USD ($) ft² property Storey | Dec. 30, 2015 USD ($) | Oct. 17, 2014 ft² property | Jul. 31, 2014 ft² property | Oct. 16, 2013 USD ($)
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rentable Square Feet | ft² |  |  | 4,300,000 |  |  |  | 4,300,000 |  |  |  |  |  |  |  |  |
Number of Properties | property |  |  | 179 |  |  |  | 179 |  |  |  |  |  |  |  |  |
Net gain (loss) on real estate venture transactions |  |  |  |  |  |  | $ 7,229,000 |  | $ (417,000) |  | $ 29,604,000 |  |  |  |  |
Gain (Loss) on Sale |  |  |  |  |  |  | $ 20,496,000 |  | $ 4,901,000 |  | $ 0 |  |  |  |  |
Office Building [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rentable Square Feet | ft² |  |  | 2,649,926 |  |  |  | 2,649,926 |  | 645,273 |  | 2,472,036 |  |  |  |  |
Number of Properties | property |  |  | 27 |  |  |  | 27 |  | 8 |  | 21 |  |  |  |  |
Gain (Loss) on Sale |  |  |  |  |  |  | $ 22,002,000 | [1],[2] | $ 4,646,000 | [3] | $ 29,233,000 | [3] |  |  |  |
Deferred gain |  |  | $ 500,000 |  |  |  | $ 500,000 |  |  |  |  |  |  |  |  |
Encino Trace [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of floors of a building | Storey |  |  | 4 |  |  |  | 4 |  |  |  |  |  |  |  |  |
Rentable Square Feet | ft² |  |  | 320,000 |  |  |  | 320,000 |  |  |  |  |  |  |  |  |
Number of Properties | property |  |  | 2 |  |  |  | 2 |  |  |  |  |  |  |  |  |
Encino Trace [Member] | Office Building [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rentable Square Feet | ft² |  |  | 320,000 |  |  |  | 320,000 |  |  |  |  |  |  |  |  |
Number of Properties | property |  |  | 2 |  |  |  | 2 |  |  |  |  |  |  |  |  |
Gain (Loss) on Sale | [1],[4] |  |  |  |  |  | $ 2,008,000 |  |  |  |  |  |  |  |  |
Carlsbad, CA [Member] | Office Building [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Provision for impairment on assets held for sale |  |  | $ 6,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Sale |  |  |  |  |  |  | $ 0 |  |  |  |  |  |  |  |  |
100 Gateway Centre Parkway [Member] | Office Building [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rentable Square Feet | ft² |  |  | 74,991 |  |  |  | 74,991 |  |  |  |  |  |  |  |  |
Number of Properties | property |  |  | 1 |  |  |  | 1 |  |  |  |  |  |  |  |  |
Provision for impairment on assets held for sale |  |  |  | $ 800,000 |  |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Sale |  |  |  | $ 0 |  |  | $ 0 | [1],[5] |  |  |  |  |  |  |  |
Lake Merritt Tower [Member] | Office Building [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rentable Square Feet | ft² |  |  | 204,336 |  |  |  | 204,336 |  |  |  |  |  |  |  |  |
Number of Properties | property |  |  | 1 |  |  |  | 1 |  |  |  |  |  |  |  |  |
Provision for impairment on assets held for sale |  |  |  |  | $ 1,700,000 |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Sale |  |  |  |  | $ 0 |  | $ 0 | [1],[6] |  |  |  |  |  |  |  |
100, 101, 200, 300 and 301 Lindenwood Drive (the Valleybrooke Poperties) [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Provision for impairment on assets held for sale |  |  |  |  |  | $ 1,800,000 |  |  |  |  |  |  |  |  |  |
100, 101, 200, 300 and 301 Lindenwood Drive (the Valleybrooke Poperties) [Member] | Office Building [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rentable Square Feet | ft² |  |  |  |  |  |  |  |  | 279,934 |  |  |  |  |  |  |
Number of Properties | property |  |  |  |  |  |  |  |  | 5 |  |  |  |  |  |  |
Gain (Loss) on Sale | [3],[7] |  |  |  |  |  |  |  | $ 203,000 |  |  |  |  |  |  |
Four Points Centre [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of floors of a building | Storey |  | 3 |  |  |  |  |  |  |  |  | 3 |  |  |  |  |
Rentable Square Feet | ft² |  |  |  |  |  |  |  |  |  |  | 192,396 |  |  |  |  |
Number of Properties | property |  | 2 |  |  |  |  |  |  |  |  | 2 |  |  |  |  |
Four Points Centre [Member] | Office Building [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rentable Square Feet | ft² |  |  |  |  |  |  |  |  | 192,396 |  |  |  |  |  |  |
Number of Properties | property |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |
Gain (Loss) on Sale | [3],[8] |  |  |  |  |  |  |  | $ (255,000) |  |  |  |  |  |  |
Austin Joint Venture [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rentable Square Feet | ft² |  |  |  |  |  |  |  |  |  |  |  |  |  | 590,881 | 232,274 |
Number of Properties | property |  |  |  |  |  |  |  |  |  |  |  |  |  | 7 | 2 |
Austin Joint Venture [Member] | Encino Trace [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Project expected cost |  |  |  |  |  |  | 91,300,000 |  |  |  |  |  |  |  |  |
Non-Recourse Debt |  |  | $ 30,000,000 |  |  |  | 30,000,000 |  |  |  |  |  |  |  |  |
Amount Of Participant Contribution |  |  | 1,800,000 |  |  |  | 1,800,000 |  |  |  |  |  |  |  |  |
Austin Joint Venture [Member] | Four Points Centre [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Non-Recourse Debt |  | $ 29,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Austin Joint Venture [Member] | Four Points Centre [Member] | Office Building [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rentable Square Feet | ft² |  | 192,396 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Brandywine Realty Trust [Member] | Austin Joint Venture [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate gross sales price of a joint venture |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 330,000,000
Brandywine Realty Trust [Member] | Austin Joint Venture [Member] | Encino Trace [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Development costs |  |  |  |  |  |  |  |  |  |  |  |  | $ 76,700,000 |  |  |
Proceeds from Equity Method Investment, Dividends or Distributions |  |  |  |  |  |  | 50,200,000 |  |  |  |  |  |  |  |  |
Capital contribution |  |  | 23,300,000 |  |  |  | 23,300,000 |  |  |  |  |  |  |  |  |
Net gain (loss) on real estate venture transactions |  |  |  |  |  |  | 2,000,000 |  |  |  |  |  |  |  |  |
Additional borrowing fund to tenant improvements and leasing commissions |  |  | 29,700,000 |  |  |  | 29,700,000 |  |  |  |  |  |  |  |  |
Brandywine Realty Trust [Member] | Austin Joint Venture [Member] | Four Points Centre [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount Of Participant Contribution |  | $ 5,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from Equity Method Investment, Dividends or Distributions |  | 34,400,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net gain (loss) on real estate venture transactions |  |  |  |  |  |  |  |  | $ (200,000) |  |  |  |  |  |  |
Aggregate gross sales price of a joint venture |  | $ 41,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
DRA Advisors LLC [Member] | Austin Joint Venture [Member] | Encino Trace [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Working capital contribution |  |  | 1,800,000 |  |  |  | 1,800,000 |  |  |  |  |  |  |  |  |
DRA Advisors LLC [Member] | Brandywine Realty Trust [Member] | Austin Joint Venture [Member] | Encino Trace [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount Of Participant Contribution |  |  | $ 25,100,000 |  |  |  | $ 25,100,000 |  |  |  |  |  |  |  |  |
[1] | Gain on Sale is net of closing and other transaction related costs.
[2] | Total gain on sale does not include a deferred gain of $0.5 million related to a prior sale.
[3] | Gain/(Loss) on Sale is net of closing and other transaction related costs.
[4] | On December 31, 2015, the Company contributed two newly constructed four-story, Class A office buildings, commonly known as “Encino Trace,” containing an aggregate of approximately 320,000 square feet in Austin, Texas to one of its existing real estate ventures (the “Austin Venture”) that the Company formed in 2013 with G&I VII Austin Office LLC, an investment vehicle advised by DRA Advisors LLC (“DRA”). When these two properties were contributed to the Austin Venture the Company had incurred a total of $76.7 million of development costs, representing the contribution value. The project is expected to cost $91.3 million with remaining costs fully funded by the Austin Venture. In conjunction with the contribution: (i) the Austin Venture obtained a $30.0 million mortgage loan; (ii) DRA contributed $25.1 million in net cash to the capital of the Austin Venture, including a $1.8 million working capital contribution; and (iii) the Austin Venture distributed $50.2 million to the Company and credited the Company with a $23.3 million capital contribution to the Austin Venture. In addition to the contribution of the properties, the Company also made a $1.8 million cash contribution to the Austin Venture for working capital. The Company recognized a $2.0 million gain on the contribution. Under the Encino Trace loan agreement the Austin Venture has the option, subject to certain leasing and loan-to-value requirements, to borrow an additional $29.7 million to fund tenant improvements and leasing commissions.
[5] | The Company recorded an impairment loss of $0.8 million for 100 Gateway Centre Parkway during the second quarter of 2015. As such, there was no gain at disposition for this property.
[6] | The Company recorded an impairment loss of $1.7 million for Lake Merritt Tower at March 31, 2015. As such, there was no gain at disposition for this property. Sales proceeds were deposited in escrow under Section 1031 of the Internal Revenue Code and applied to purchase the Broadmoor Austin portfolio. Refer to Broadmoor Austin Associates acquisition summary, above, for further details.
[7] | During the third quarter of 2014, the Company recorded a $1.8 million impairment loss on these properties.
[8] | On April 3, 2014, the Company contributed two three-story, Class A office buildings, commonly known as “Four Points Centre,” containing an aggregate of approximately 192,396 net rentable square feet in Austin, Texas to an existing real estate venture (the “Austin Venture”) that the Company formed in 2013 with G&I VII Austin Office LLC, an investment vehicle advised by DRA Advisors LLC (“DRA”). The Company contributed the properties to the Austin Venture at an agreed upon value of $41.5 million. In conjunction with the contribution: (i) the Austin Venture obtained a $29.0 million mortgage loan; (ii) DRA contributed $5.9 million in net cash to the capital of the Austin Venture; and (iii) the Austin Venture distributed $34.4 million to the Company and credited the Company with a $5.9 million capital contribution to the Austin Venture. The Company incurred a $0.2 million loss on the contribution, driven primarily by closing costs.

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