Schedule of ARM Securities Forward Purchase Commitments (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Forward purchase agreements - Face/UPB	$ 3,804,615	$ 2,826,769
Forward purchase agreements - Cost	3,930,324	2,911,197
Forward purchase agreements - Fair Value	3,950,525	2,879,014
Forward purchase agreements - Net Asset (Liability)	20,201	(32,183)
ARMs - Originators
Derivative [Line Items]
Forward purchase agreements - Face/UPB	173,605	145,246
Forward purchase agreements - Cost	177,117	147,749
Forward purchase agreements - Fair Value	178,699	147,914
Forward purchase agreements - Net Asset (Liability)	1,582	165
Fixed-rate TBA Dollar Roll Securities
Derivative [Line Items]
Forward purchase agreements - Face/UPB	3,617,000	2,655,000
Forward purchase agreements - Cost	3,739,204	2,736,748
Forward purchase agreements - Fair Value	3,757,772	2,704,375
Forward purchase agreements - Net Asset (Liability)	18,568	(32,373)
Whole Mortgage Loans
Derivative [Line Items]
Forward purchase agreements - Face/UPB	14,010	26,523
Forward purchase agreements - Cost	14,003	26,700
Forward purchase agreements - Fair Value	14,054	26,725
Forward purchase agreements - Net Asset (Liability)	$ 51	$ 25