Debt (Summary of Outstanding and Carrying Value of Collateral by Asset Type) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Outstanding Balance	$ 8,474,300	$ 8,059,802
Other Debt [Member]
Debt Instrument [Line Items]
Outstanding Balance	28,443
Collateral Carrying Value	59,454
Other Debt [Member] | Mortgage notes receivable [Member]
Debt Instrument [Line Items]
Outstanding Balance	7,858
Collateral Carrying Value	19,705
Other Debt [Member] | Intercompany mortgage loans [Member]
Debt Instrument [Line Items]
Outstanding Balance	2,198
Collateral Carrying Value	5,144
Other Debt [Member] | CMBS [Member]
Debt Instrument [Line Items]
Outstanding Balance	18,387
Collateral Carrying Value	$ 34,605