Variable Interest Entities (Details) $ in Thousands		12 Months Ended
	Mar. 31, 2016 USD ($) trust	Dec. 31, 2016 USD ($) item	Dec. 31, 2015 USD ($)
Variable interest entities
VIE Assets		$ 67,123,261	$ 76,675,689
VIE Liabilities		66,130,592	75,817,014
Investment securities		807,618	724,947
Debt obligations to beneficial interest holders, unpaid principal balances		2,053,229	1,372,594
Interest in VIE		204,605	$ 199,201
Primary beneficiary | Accounting Standards Update 2015-02
Variable interest entities
VIE Assets		184,500
VIE Liabilities		$ 110,100
Primary beneficiary | Accounting Standards Update 2015-02 | Adjustment
Variable interest entities
Number of VIE's | trust	14
VIE Assets	$ 15,100,000
VIE Liabilities	15,100,000
Not primary beneficiary
Variable interest entities
Number of CDO structures currently in default | item		1
Maximum risk of loss related to VIEs, on fair value basis		$ 31,500
Not primary beneficiary | Accounting Standards Update 2015-02
Variable interest entities
Maximum risk of loss related to VIEs, on fair value basis		134,200
Interest in VIE		134,200
Commitments on loss		25,700
Not primary beneficiary | Securitization SPEs
Variable interest entities
Debt obligations to beneficial interest holders, unpaid principal balances		$ 13,100,000
CMBS | Primary beneficiary | Accounting Standards Update 2015-02
Variable interest entities
Carrying value	$ 120,900