Schedule of ARM Securities Forward Purchase Commitments (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Derivative [Line Items]
Forward purchase agreements - Face/UPB	$ 2,940,069	$ 3,808,687
Forward purchase agreements - Cost	3,027,845	3,927,034
Forward purchase agreements - Fair Value	3,028,643	3,943,097
Forward purchase agreements - Net Asset (Liability)	798	16,063
ARMs - Originators
Derivative [Line Items]
Forward purchase agreements - Face/UPB	205,275	376,936
Forward purchase agreements - Cost	209,881	384,673
Forward purchase agreements - Fair Value	211,990	388,829
Forward purchase agreements - Net Asset (Liability)	2,109	4,156
15-year TBA Dollar Roll Securities
Derivative [Line Items]
Forward purchase agreements - Face/UPB	2,655,000	3,400,000
Forward purchase agreements - Cost	2,736,748	3,509,871
Forward purchase agreements - Fair Value	2,735,012	3,521,816
Forward purchase agreements - Net Asset (Liability)	(1,736)	11,945
Whole Mortgage Loans
Derivative [Line Items]
Forward purchase agreements - Face/UPB	79,794	11,656
Forward purchase agreements - Cost	81,216	11,937
Forward purchase agreements - Fair Value	81,641	11,935
Forward purchase agreements - Net Asset (Liability)	$ 425	(2)
ARMs - Dealers
Derivative [Line Items]
Forward purchase agreements - Face/UPB		20,095
Forward purchase agreements - Cost		20,553
Forward purchase agreements - Fair Value		20,517
Forward purchase agreements - Net Asset (Liability)		$ (36)