Real Estate Activities Real Estate Activities - Impairment of Assets (Details) - USD ($) $ in Thousands	1 Months Ended			3 Months Ended		9 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Schedule of Asset Impairments [Line Items]
Asset Impairment Charges				$ 9,865	$ 51,412	$ 24,589	$ 86,319
Impairment of assets and expensed project costs						$ 24,589	$ 86,648
Washington Crown Center [Member]
Schedule of Asset Impairments [Line Items]
Impairment of assets and expensed project costs	$ 9,900	$ 14,100
Voorhees office building [Member]
Schedule of Asset Impairments [Line Items]
Impairment of assets and expensed project costs			$ 600