Debt (Summary of Outstanding and Carrying Value of Collateral by Asset Type) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Outstanding Balance	$ 8,966,996	$ 10,513,781
Other Debt [Member]
Debt Instrument [Line Items]
Outstanding Balance	35,137
Collateral Carrying Value	68,303
Other Debt [Member] | Loans held for investment [Member]
Debt Instrument [Line Items]
Outstanding Balance	9,708
Collateral Carrying Value	20,428
Other Debt [Member] | Intercompany mortgage loans [Member]
Debt Instrument [Line Items]
Outstanding Balance	2,715
Collateral Carrying Value	8,013
Other Debt [Member] | CMBS [Member]
Debt Instrument [Line Items]
Outstanding Balance	22,714
Collateral Carrying Value	$ 39,862