Use of Special Purpose Entities (SPE) and Variable Interest Entities (VIE) - Narrative (Details) $ in Millions	Dec. 31, 2015 USD ($) securitization	Dec. 31, 2014 USD ($) securitization
Variable Interest Entity [Line Items]
Unconsolidated VIE, maximum loss exposure | $	$ 170.7	$ 111.5
Residential mortgage loans held in securitization trusts
Variable Interest Entity [Line Items]
Number of securitizations completed to date	4
Number of securitizations, accounted for as permanent financing	3
K-Series | Consolidated K-Series
Variable Interest Entity [Line Items]
Number of securitizations	5	6
K-Series | Non-Financings, Multi-Family CMBS
Variable Interest Entity [Line Items]
Number of securitizations considered non-financing VIEs	1	2
K-Series | Multi-Family Collateralized Mortgage Backed Securities
Variable Interest Entity [Line Items]
Number of securitizations	2	2