Schedule of ARM Securities Forward Purchase Commitments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Forward purchase agreements - Face/UPB	$ 4,815,786	$ 3,808,687
Forward purchase agreements - Cost	4,967,992	3,927,034
Forward purchase agreements - Fair Value	4,999,466	3,943,097
Forward purchase agreements - Net Asset (Liability)	31,474	16,063
Whole mortgage loans
Derivative [Line Items]
Forward purchase agreements - Face/UPB	71,409	11,656
Forward purchase agreements - Cost	73,034	11,937
Forward purchase agreements - Fair Value	73,363	11,935
Forward purchase agreements - Net Asset (Liability)	329	(2)
ARMs - Originators
Derivative [Line Items]
Forward purchase agreements - Face/UPB	349,377	376,936
Forward purchase agreements - Cost	357,082	384,673
Forward purchase agreements - Fair Value	360,836	388,829
Forward purchase agreements - Net Asset (Liability)	3,754	4,156
ARMs - Dealers
Derivative [Line Items]
Forward purchase agreements - Face/UPB	95,000	20,095
Forward purchase agreements - Cost	97,208	20,553
Forward purchase agreements - Fair Value	98,302	20,517
Forward purchase agreements - Net Asset (Liability)	1,094	(36)
15-year TBA Dollar Roll Securities
Derivative [Line Items]
Forward purchase agreements - Face/UPB	4,300,000	3,400,000
Forward purchase agreements - Cost	4,440,668	3,509,871
Forward purchase agreements - Fair Value	4,466,965	3,521,816
Forward purchase agreements - Net Asset (Liability)	$ 26,297	$ 11,945