Debt (Summary of Outstanding and Carrying Value of Collateral by Asset Type) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Outstanding Balance	$ 7,802,565	$ 8,059,802
Other Debt [Member]
Debt Instrument [Line Items]
Outstanding Balance	29,300
Collateral Carrying Value	61,333
Other Debt [Member] | Mortgage notes receivable [Member]
Debt Instrument [Line Items]
Outstanding Balance	8,095
Collateral Carrying Value	19,950
Other Debt [Member] | Intercompany mortgage loans [Member]
Debt Instrument [Line Items]
Outstanding Balance	2,264
Collateral Carrying Value	5,462
Other Debt [Member] | CMBS [Member]
Debt Instrument [Line Items]
Outstanding Balance	18,941
Collateral Carrying Value	$ 35,921