Real Estate Investments - Summary of Properties Classified as Held for Sale Included in Continuing Operations (Details) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
ASSETS HELD FOR SALE
Total assets held for sale, net		$ 41,718	$ 584,365
LIABILITIES HELD FOR SALE
Total liabilities held for sale		81	2,151
Held for Sale Properties Included in Continuing Operations [Member]
ASSETS HELD FOR SALE
Operating properties		73,591	794,588
Accumulated depreciation		(32,916)	(213,581)
Operating real estate investments, net		40,675	581,007
Construction-in-progress			1,940
Land held for development		1,043	837
Total real estate investments, net		41,718	583,784
Intangible assets			581
Total assets held for sale, net		41,718	584,365
LIABILITIES HELD FOR SALE
Acquired lease intangibles, net			192
Other liabilities		81	1,959
Total liabilities held for sale		81	2,151
Held for Sale Properties Included in Continuing Operations [Member] | Metropolitan D.C. - Office [Member]
ASSETS HELD FOR SALE
Operating properties	[1]	21,720
Accumulated depreciation	[1]	(11,935)
Operating real estate investments, net	[1]	9,785
Land held for development	[1]	0
Total real estate investments, net	[1]	9,785
Total assets held for sale, net	[1]	9,785
LIABILITIES HELD FOR SALE
Other liabilities	[1]	73
Total liabilities held for sale	[1]	73
Held for Sale Properties Included in Continuing Operations [Member] | Other Segment - Office [Member]
ASSETS HELD FOR SALE
Operating properties	[2]	51,871
Accumulated depreciation	[2]	(20,981)
Operating real estate investments, net	[2]	30,890
Land held for development	[2]	0
Total real estate investments, net	[2]	30,890
Total assets held for sale, net	[2]	30,890
LIABILITIES HELD FOR SALE
Other liabilities	[2]	8
Total liabilities held for sale	[2]	8
Held for Sale Properties Included in Continuing Operations [Member] | Other Segment - Land [Member]
ASSETS HELD FOR SALE
Operating properties	[3]	0
Accumulated depreciation	[3]	0
Operating real estate investments, net	[3]	0
Land held for development	[3]	1,043
Total real estate investments, net	[3]	1,043
Total assets held for sale, net	[3]	1,043
LIABILITIES HELD FOR SALE
Other liabilities	[3]	0
Total liabilities held for sale	[3]	$ 0
Held for Sale Properties Included in Continuing Operations [Member] | Och Ziff Properties [Member]
ASSETS HELD FOR SALE
Operating properties	[4]		526,099
Accumulated depreciation	[4]		(179,092)
Operating real estate investments, net	[4]		347,007
Construction-in-progress	[4]		1,915
Land held for development	[4]		0
Total real estate investments, net	[4]		348,922
Intangible assets	[4]		581
Total assets held for sale, net	[4]		349,503
LIABILITIES HELD FOR SALE
Acquired lease intangibles, net	[4]		192
Other liabilities	[4]		1,959
Total liabilities held for sale	[4]		2,151
Held for Sale Properties Included in Continuing Operations [Member] | 2970 Market Street (Cira Square) [Member]
ASSETS HELD FOR SALE
Operating properties	[5]		268,489
Accumulated depreciation	[5]		(34,489)
Operating real estate investments, net	[5]		234,000
Construction-in-progress	[5]		25
Land held for development	[5]		0
Total real estate investments, net	[5]		234,025
Intangible assets	[5]		0
Total assets held for sale, net	[5]		234,025
LIABILITIES HELD FOR SALE
Acquired lease intangibles, net	[5]		0
Other liabilities	[5]		0
Total liabilities held for sale	[5]		0
Held for Sale Properties Included in Continuing Operations [Member] | Greenhills Land [Member]
ASSETS HELD FOR SALE
Operating properties	[6]		0
Accumulated depreciation	[6]		0
Operating real estate investments, net	[6]		0
Construction-in-progress	[6]		0
Land held for development	[6]		837
Total real estate investments, net	[6]		837
Intangible assets	[6]		0
Total assets held for sale, net	[6]		837
LIABILITIES HELD FOR SALE
Acquired lease intangibles, net	[6]		0
Other liabilities	[6]		0
Total liabilities held for sale	[6]		$ 0

[1] As of December 31, 2016, the Company determined that the sale of three office properties in the Metropolitan D.C. segment was probable and classified these properties as held for sale in accordance with applicable accounting standards for long lived assets. At such date, the carrying value of the properties exceeded their fair value less the anticipated costs of sale. As a result, the Company recognized an impairment loss totaling approximately $3.0 million during the three-month period ended December 31, 2016. The Company measured this impairment based on a discounted cash flow analysis, using a hold period of 10 years and residual capitalization rates and discount rates of 9.00% and 10.00%, respectively. The results were comparable to indicative pricing in the market. As significant inputs to the model are unobservable, the Company determined that the value determined for this property falls within Level 3 fair value reporting.

[2] As of December 31, 2016, the Company determined that the sale of two office properties in the Other segment was probable and classified these properties as held for sale in accordance with applicable accounting standards for long lived assets. At such date, the carrying value of the properties exceeded the fair value less the anticipated costs of sale. As a result, the Company recognized an impairment loss totaling approximately $11.5 million during the three-month period ended December 31, 2016. The Company measured this impairment based on a discounted cash flow analysis, using a hold period of 10 years and residual capitalization rates and discount rates of 9.75% and 9.75%, respectively. The results were comparable to indicative pricing in the market. As significant inputs to the model are unobservable, the Company determined that the value determined for this property falls within Level 3 fair value reporting.

[3] As of December 31, 2016, the Company determined that the sale of a land parcel in the Other segment was probable and classified the land parcel as held for sale in accordance with applicable accounting standards for long lived assets. At such date, the carrying value of the land approximated the fair value less the anticipated costs of sale and the Company recorded a nominal impairment. The fair value measurement was based on the pricing in the purchase and sale.

[4] On February 4, 2016, the Company disposed of its interests in 58 properties located in the Pennsylvania Suburbs, New Jersey/Delaware, Metropolitan Washington, D.C. and Richmond, Virginia segments in a series of related transactions with Och Ziff Real Estate. During the fourth quarter of 2015, significant provisions were agreed upon by both the Company and Och Ziff Real Estate and, as a result, the Company determined that the sale of the portfolio was probable and classified these properties as held for sale in accordance with applicable accounting standards for long lived assets. At such date, the carrying value of the properties exceeded the fair value less the anticipated costs of sale. As a result, the Company recognized an impairment loss totaling approximately $45.4 million during the year ended December 31, 2015. The fair value measurement was based on the pricing in the purchase and sale agreement. As the significant inputs to the model are unobservable, the Company determined that the value determined for these real estate investments fall within Level 3 for fair value reporting.

[5] On December 23, 2015 the Company entered into a purchase and sale agreement to dispose of its equity interests in the office property located at 2970 Market Street in Philadelphia commonly known as 30th Street Main Post Office (“Cira Square”), which includes 862,692 square feet of rentable space and is fully leased to a single tenant. As of December 31, 2015, the Company determined the sale was probable and classified the property as held for sale in accordance with applicable accounting standards for long lived assets. As the fair value less anticipated costs to sell exceeded the carrying value of the property no impairment loss was recorded. The fair value measurement was based on the pricing in the purchase and sale agreement. As the sales price is unobservable, the Company determined that the significant inputs used to value this real estate investment falls within Level 3 for fair value reporting. On February 5, 2016 the Company completed the disposition of its equity interests in Cira Square.

[6] On January 15, 2016, the Company sold the fee interest in a 120 acre land parcel located in Berks County, Pennsylvania for $0.9 million. As of December 31, 2015, the Company classified this land parcel as held for sale in accordance with the applicable accounting standards for long lived assets. At such date, the carrying value of the properties exceeded the fair value less the anticipated costs of sale. As a result, the Company recognized an impairment loss totaling approximately $0.3 million during the year ended December 31, 2015.