Property Dispositions, Discontinued Operations and Real Estate Impairment (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) Property	Sep. 30, 2014 USD ($) Property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment of real estate			$ 32,931	$ 11,062
Debt satisfaction gains (charges), net	$ (398)	$ (455)	13,753	(7,946)
Other asset impairment charges			1,139	18,864
Impaired real estate investment property, at cost	$ 475	$ 5,574	475	5,574
Mortgages [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt extinguishment amount			30,293	9,900
Sold Properties [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Aggregate gross disposition price			217,675	105,180
Gain on sale of properties			24,884	$ 22,052
Transferred Property [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real estate number of properties transferred | Property				1
Debt satisfaction gains (charges), net			$ 10,106	$ (299)
Office Building [Member] | Transferred Property [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real estate number of properties transferred | Property			2