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Real Estate Investments - Summary of Office Properties Sold (Details) |  | 3 Months Ended | 12 Months Ended |
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Feb. 04, 2016 property | Jun. 30, 2015 USD ($) | Mar. 31, 2015 USD ($) | Dec. 31, 2016 USD ($) ft² property | Dec. 31, 2015 USD ($) ft² property | Dec. 31, 2014 USD ($) ft² property | Dec. 23, 2015 ft²
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Proceeds from the sale of properties |  |  |  |  | $ 784,331,000 |  | $ 247,228,000 |  | $ 118,855,000 |  |
Gain (Loss) on Sale |  |  |  |  | $ 116,983,000 |  | $ 20,496,000 |  | $ 4,901,000 |  |
2970 Market Street (Cira Square) [Member] |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Rentable Square Feet | ft² |  |  |  |  |  |  |  |  |  |  | 862,692
Encino Trace [Member] |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Properties Sold | property |  |  |  |  |  |  | 2 |  |  |  |
Rentable Square Feet | ft² |  |  |  |  |  |  | 320,000 |  |  |  |
11305 Four Points Drive (Four Points Centre) [Member] |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Properties Sold | property |  |  |  |  |  |  |  |  | 2 |  |
Rentable Square Feet | ft² |  |  |  |  |  |  |  |  | 192,396 |  |
Office Properties [Member] |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Properties Sold | property |  |  |  |  | 66 |  | 27 |  | 8 |  |
Rentable Square Feet | ft² |  |  |  |  | 5,239,632 |  | 2,649,926 |  | 645,273 |  |
Sales Price |  |  |  |  | $ 820,000,000 |  | $ 374,600,000 |  | $ 101,150,000 |  |
Proceeds from the sale of properties |  |  |  |  | 769,799,000 |  | 340,098,000 |  | 113,024,000 |  |
Gain (Loss) on Sale |  |  |  |  | $ 116,983,000 | [1] | $ 22,002,000 | [2],[3] | $ 4,646,000 | [4] |
Office Properties [Member] | 620, 640, 660 Allendale Road [Member] |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Properties Sold | property |  |  |  |  | 3 |  |  |  |  |  |
Rentable Square Feet | ft² |  |  |  |  | 156,669 |  |  |  |  |  |
Sales Price |  |  |  |  | $ 12,800,000 |  |  |  |  |  |
Proceeds from the sale of properties |  |  |  |  | 12,014,000 |  |  |  |  |  |
Gain (Loss) on Sale | [1] |  |  |  | $ 2,382,000 |  |  |  |  |  |
Office Properties [Member] | 1120 Executive Plaza [Member] |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Properties Sold | property |  |  |  |  | 1 |  |  |  |  |  |
Rentable Square Feet | ft² |  |  |  |  | 95,183 |  |  |  |  |  |
Sales Price |  |  |  |  | $ 9,500,000 |  |  |  |  |  |
Proceeds from the sale of properties |  |  |  |  | 9,241,000 |  |  |  |  |  |
Gain (Loss) on Sale | [1],[5] |  |  |  | $ (18,000) |  |  |  |  |  |
Office Properties [Member] | 50 East Clementon Road [Member] |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Properties Sold | property |  |  |  |  | 1 |  |  |  |  |  |
Rentable Square Feet | ft² |  |  |  |  | 3,080 |  |  |  |  |  |
Sales Price |  |  |  |  | $ 1,100,000 |  |  |  |  |  |
Proceeds from the sale of properties |  |  |  |  | 1,011,000 |  |  |  |  |  |
Gain (Loss) on Sale | [1] |  |  |  | $ (85,000) |  |  |  |  |  |
Office Properties [Member] | 196/198 Van Buren Street (Herndon Metro Plaza I&II) [Member] |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Properties Sold | property |  |  |  |  | 2 |  |  |  |  |  |
Rentable Square Feet | ft² |  |  |  |  | 197,225 |  |  |  |  |  |
Sales Price |  |  |  |  | $ 44,500,000 |  |  |  |  |  |
Proceeds from the sale of properties |  |  |  |  | 43,412,000 |  |  |  |  |  |
Gain (Loss) on Sale | [1],[6] |  |  |  | $ (752,000) |  |  |  |  |  |
Office Properties [Member] | 2970 Market Street (Cira Square) [Member] |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Properties Sold | property |  |  |  |  | 1 |  |  |  |  |  |
Rentable Square Feet | ft² |  |  |  |  | 862,692 |  |  |  |  |  |
Sales Price |  |  |  |  | $ 354,000,000 |  |  |  |  |  |
Proceeds from the sale of properties |  |  |  |  | 350,150,000 |  |  |  |  |  |
Gain (Loss) on Sale | [1] |  |  |  | $ 115,828,000 |  |  |  |  |  |
Office Properties [Member] | Och Ziff Portfolio [Member] |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Properties Sold | property |  | 58 |  |  | 58 | [7] |  |  |  |  |
Rentable Square Feet | ft² | [7] |  |  |  | 3,924,783 |  |  |  |  |  |
Sales Price | [7] |  |  |  | $ 398,100,000 |  |  |  |  |  |
Proceeds from the sale of properties | [7] |  |  |  | 353,971,000 |  |  |  |  |  |
Gain (Loss) on Sale | [1],[7],[8] |  |  |  | $ (372,000) |  |  |  |  |  |
Office Properties [Member] | Encino Trace [Member] |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Properties Sold | property |  |  |  |  |  |  | 2 |  |  |  |
Rentable Square Feet | ft² |  |  |  |  |  |  | 320,000 |  |  |  |
Sales Price |  |  |  |  |  |  | $ 76,700,000 |  |  |  |
Proceeds from the sale of properties |  |  |  |  |  |  | 50,158,000 |  |  |  |
Gain (Loss) on Sale | [2],[9] |  |  |  |  |  | $ 2,008,000 |  |  |  |
Office Properties [Member] | Laurel Corporate Center [Member] |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Properties Sold | property |  |  |  |  |  |  | 6 |  |  |  |
Rentable Square Feet | ft² |  |  |  |  |  |  | 560,147 |  |  |  |
Sales Price |  |  |  |  |  |  | $ 56,500,000 |  |  |  |
Proceeds from the sale of properties |  |  |  |  |  |  | 56,253,000 |  |  |  |
Gain (Loss) on Sale | [2] |  |  |  |  |  | $ 2,901,000 |  |  |  |
Office Properties [Member] | Carlsbad Properties [Member] |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Properties Sold | property |  |  |  |  |  |  | 3 |  |  |  |
Rentable Square Feet | ft² |  |  |  |  |  |  | 196,075 |  |  |  |
Sales Price |  |  |  |  |  |  | $ 30,400,000 |  |  |  |
Proceeds from the sale of properties |  |  |  |  |  |  | 29,568,000 |  |  |  |
Gain (Loss) on Sale | [2],[10] |  |  |  |  |  | $ 0 |  |  |  |
Office Properties [Member] | 751-761 Fifth Ave [Member] |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Properties Sold | property |  |  |  |  |  |  | 1 |  |  |  |
Rentable Square Feet | ft² |  |  |  |  |  |  | 158,000 |  |  |  |
Sales Price |  |  |  |  |  |  | $ 4,600,000 |  |  |  |
Proceeds from the sale of properties |  |  |  |  |  |  | 4,245,000 |  |  |  |
Gain (Loss) on Sale | [2] |  |  |  |  |  | $ 894,000 |  |  |  |
Office Properties [Member] | 1000 Howard Boulevard [Member] |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Properties Sold | property |  |  |  |  |  |  | 1 |  |  |  |
Rentable Square Feet | ft² |  |  |  |  |  |  | 105,312 |  |  |  |
Sales Price |  |  |  |  |  |  | $ 16,500,000 |  |  |  |
Proceeds from the sale of properties |  |  |  |  |  |  | 15,780,000 |  |  |  |
Gain (Loss) on Sale | [2] |  |  |  |  |  | $ 4,828,000 |  |  |  |
Office Properties [Member] | Bay Colony Office Park [Member] |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Properties Sold | property |  |  |  |  |  |  | 4 |  |  |  |
Rentable Square Feet | ft² |  |  |  |  |  |  | 247,294 |  |  |  |
Sales Price |  |  |  |  |  |  | $ 37,500,000 |  |  |  |
Proceeds from the sale of properties |  |  |  |  |  |  | 36,386,000 |  |  |  |
Gain (Loss) on Sale | [2] |  |  |  |  |  | $ 269,000 |  |  |  |
Office Properties [Member] | 741 First Avenue [Member] |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Properties Sold | property |  |  |  |  |  |  | 1 |  |  |  |
Rentable Square Feet | ft² |  |  |  |  |  |  | 77,184 |  |  |  |
Sales Price |  |  |  |  |  |  | $ 4,900,000 |  |  |  |
Proceeds from the sale of properties |  |  |  |  |  |  | 4,640,000 |  |  |  |
Gain (Loss) on Sale | [2] |  |  |  |  |  | $ 372,000 |  |  |  |
Office Properties [Member] | 100 Gateway Centre Parkway [Member] |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Properties Sold | property |  |  |  |  |  |  | 1 |  |  |  |
Rentable Square Feet | ft² |  |  |  |  |  |  | 74,991 |  |  |  |
Sales Price |  |  |  |  |  |  | $ 4,100,000 |  |  |  |
Proceeds from the sale of properties |  |  |  |  |  |  | 3,911,000 |  |  |  |
Gain (Loss) on Sale |  |  | $ 0 |  |  |  | $ 0 | [2],[11] |  |  |
Office Properties [Member] | Christina & Delaware Corporate Centers [Member] |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Properties Sold | property |  |  |  |  |  |  | 5 |  |  |  |
Rentable Square Feet | ft² |  |  |  |  |  |  | 485,182 |  |  |  |
Sales Price |  |  |  |  |  |  | $ 50,100,000 |  |  |  |
Proceeds from the sale of properties |  |  |  |  |  |  | 49,579,000 |  |  |  |
Gain (Loss) on Sale | [2] |  |  |  |  |  | $ 1,749,000 |  |  |  |
Office Properties [Member] | Lake Merritt Tower [Member] |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Properties Sold | property |  |  |  |  |  |  | 1 |  |  |  |
Rentable Square Feet | ft² |  |  |  |  |  |  | 204,336 |  |  |  |
Sales Price |  |  |  |  |  |  | $ 65,000,000 |  |  |  |
Proceeds from the sale of properties |  |  |  |  |  |  | 62,800,000 |  |  |  |
Gain (Loss) on Sale |  |  |  | $ 0 |  |  | $ 0 | [2],[12] |  |  |
Office Properties [Member] | 1000 Atrium Way / 457 Haddonfield Road (Atrium I / Libertyview) [Member] |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Properties Sold | property |  |  |  |  |  |  | 2 |  |  |  |
Rentable Square Feet | ft² |  |  |  |  |  |  | 221,405 |  |  |  |
Sales Price |  |  |  |  |  |  | $ 28,300,000 |  |  |  |
Proceeds from the sale of properties |  |  |  |  |  |  | 26,778,000 |  |  |  |
Gain (Loss) on Sale | [2] |  |  |  |  |  | $ 8,981,000 |  |  |  |
Office Properties [Member] | 100, 101, 200, 300 and 301 Lindenwood Drive (the Valleybrooke Properties) [Member] |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Properties Sold | property |  |  |  |  |  |  |  |  | 5 |  |
Rentable Square Feet | ft² |  |  |  |  |  |  |  |  | 279,934 |  |
Sales Price |  |  |  |  |  |  |  |  | $ 37,900,000 |  |
Proceeds from the sale of properties |  |  |  |  |  |  |  |  | 37,156,000 |  |
Gain (Loss) on Sale | [4],[13] |  |  |  |  |  |  |  | $ 203,000 |  |
Office Properties [Member] | 1880 Campus Commons Drive (Campus Pointe) [Member] |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Properties Sold | property |  |  |  |  |  |  |  |  | 1 |  |
Rentable Square Feet | ft² |  |  |  |  |  |  |  |  | 172,943 |  |
Sales Price |  |  |  |  |  |  |  |  | $ 42,500,000 |  |
Proceeds from the sale of properties |  |  |  |  |  |  |  |  | 41,476,000 |  |
Gain (Loss) on Sale | [4] |  |  |  |  |  |  |  | $ 4,698,000 |  |
Office Properties [Member] | 11305 Four Points Drive (Four Points Centre) [Member] |  |  |  |  |  |  |  |  |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of Properties Sold | property |  |  |  |  |  |  |  |  | 2 |  |
Rentable Square Feet | ft² |  |  |  |  |  |  |  |  | 192,396 |  |
Sales Price |  |  |  |  |  |  |  |  | $ 20,750,000 |  |
Proceeds from the sale of properties |  |  |  |  |  |  |  |  | 34,392,000 |  |
Gain (Loss) on Sale | [4],[14] |  |  |  |  |  |  |  | $ (255,000) |  |
[1] | Gain/(Loss) on Sale is net of closing and other transaction related costs.
[2] | Gain on Sale is net of closing and other transaction related costs.
[3] | Total gain on sale does not include a deferred gain of $0.5 million related to a prior sale.
[4] | Gain/(Loss) on sale is net of closing and other transaction related costs.
[5] | As of June 30, 2016, the Company determined that the sale of the property was probable and classified this property as held for sale in accordance with applicable accounting standards for long lived assets. At such date, the carrying value of the property exceeded the fair value less the anticipated costs of sale. As a result, the Company recognized a provision for impairment totaling approximately $1.8 million during the three-month period ended June 30, 2016. The fair value measurement was based on the pricing in the purchase and sale agreement for the sale of the property. As the pricing in the purchase and sale agreement is unobservable, the Company determined that the inputs utilized to determine fair value for this property falls within Level 3 in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, "Fair Value Measurements and Disclosures.” The loss on sale represents additional closing costs recognized at closing.
[6] | During the three-month period ended March 31, 2016, the Company recognized a provision for impairment totaling approximately $7.4 million on the properties. See “Held for Use Impairment” section below. The loss on sale primarily relates to additional closing costs recognized at closing.
[7] | Exhibit 99.2 to the Company’s Current Report on Form 8-K filed on February 10, 2016 contains a complete list of the 58 properties disposed of in the transactions with Och-Ziff Capital Management Group LLC. See Note 4, "Investment in Unconsolidated Real Estate Ventures," for further details of the transactions.
[8] | During the three-month period ended December 31, 2015, the Company recognized a provision for impairment totaling approximately $45.4 million. The loss on sale represents additional closing costs recognized at closing.
[9] | 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.
[10] | The Company recorded an impairment loss of $6.3 million for the Carlsbad office properties during the fourth quarter of 2015. As such, there was no gain at disposition for this property.
[11] | 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.
[12] | 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.
[13] | During the third quarter of 2014, the Company recorded a $1.8 million impairment loss on these properties.
[14] | 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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