MBS and CRT Securities (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Schedule of MBS and CRT Securities [Line Items]
Minimum term of fixed rate mortgages underlying MBS	15 years
Principal/ Current Face	$ 12,603,050	$ 11,039,694
Purchase Premiums	192,676	213,790
Accretable Purchase Discounts	(367,422)	(404,362)
Discount Designated as Credit Reserve and OTTI	(847,017)	(900,557)
Amortized Cost	11,582,613	9,949,107
Fair Value	12,342,274	10,762,622
Gross Unrealized Gains	799,247	852,963
Gross Unrealized Losses	(39,586)	(39,448)
Net Unrealized Gain/(Loss)	759,661	813,515
Principal payments receivable	1,300	542
Linked Transactions
Schedule of MBS and CRT Securities [Line Items]
Par/Current Face		1,926,987
Amortized Cost		1,913,276
Fair Value		1,917,813
Total MBS
Schedule of MBS and CRT Securities [Line Items]
Principal/ Current Face	12,472,050	10,930,194
Purchase Premiums	192,676	213,790
Accretable Purchase Discounts	(363,011)	(399,635)
Discount Designated as Credit Reserve and OTTI	(847,017)	(900,557)
Amortized Cost	11,456,024	9,844,334
Fair Value	12,213,364	10,659,639
Gross Unrealized Gains	796,432	852,639
Gross Unrealized Losses	(39,092)	(37,334)
Net Unrealized Gain/(Loss)	757,340	815,305
Agency Mortgage Backed Securities
Schedule of MBS and CRT Securities [Line Items]
Principal/ Current Face	5,069,854	5,610,293
Purchase Premiums	192,347	213,329
Accretable Purchase Discounts	(65)	(71)
Discount Designated as Credit Reserve and OTTI	0	0
Amortized Cost	5,263,462	5,824,093
Fair Value	5,331,211	5,904,207
Gross Unrealized Gains	101,195	113,736
Gross Unrealized Losses	(33,446)	(33,622)
Net Unrealized Gain/(Loss)	67,749	80,114
Agency Mortgage Backed Securities | Fannie Mae
Schedule of MBS and CRT Securities [Line Items]
Principal/ Current Face	4,127,078	4,587,823
Purchase Premiums	156,323	174,245
Accretable Purchase Discounts	(65)	(71)
Discount Designated as Credit Reserve and OTTI	0	0
Amortized Cost	4,283,336	4,761,997
Fair Value	4,354,077	4,843,084
Gross Unrealized Gains	91,055	102,187
Gross Unrealized Losses	(20,314)	(21,100)
Net Unrealized Gain/(Loss)	70,741	81,087
Agency Mortgage Backed Securities | Freddie Mac
Schedule of MBS and CRT Securities [Line Items]
Principal/ Current Face	932,698	1,011,659
Purchase Premiums	35,848	38,895
Accretable Purchase Discounts	0	0
Discount Designated as Credit Reserve and OTTI	0	0
Amortized Cost	969,872	1,051,096
Fair Value	966,618	1,049,854
Gross Unrealized Gains	9,878	11,280
Gross Unrealized Losses	(13,132)	(12,522)
Net Unrealized Gain/(Loss)	(3,254)	(1,242)
Agency Mortgage Backed Securities | Ginnie Mae
Schedule of MBS and CRT Securities [Line Items]
Principal/ Current Face	10,078	10,811
Purchase Premiums	176	189
Accretable Purchase Discounts	0	0
Discount Designated as Credit Reserve and OTTI	0	0
Amortized Cost	10,254	11,000
Fair Value	10,516	11,269
Gross Unrealized Gains	262	269
Gross Unrealized Losses	0	0
Net Unrealized Gain/(Loss)	262	269
Non-Agency MBS
Schedule of MBS and CRT Securities [Line Items]
Principal/ Current Face	7,402,196	5,319,901
Purchase Premiums	329	461
Accretable Purchase Discounts	(362,946)	(399,564)
Discount Designated as Credit Reserve and OTTI	(847,017)	(900,557)
Amortized Cost	6,192,562	4,020,241
Fair Value	6,882,153	4,755,432
Gross Unrealized Gains	695,237	738,903
Gross Unrealized Losses	(5,646)	(3,712)
Net Unrealized Gain/(Loss)	689,591	735,191
Credit Reserve	824,800	877,600
OTTI	22,200	23,000
Non-Agency MBS | Expected to Recover Par
Schedule of MBS and CRT Securities [Line Items]
Principal/ Current Face	2,870,432	431,788
Purchase Premiums	329	461
Accretable Purchase Discounts	(30,932)	(29,501)
Discount Designated as Credit Reserve and OTTI	0	0
Amortized Cost	2,839,829	402,748
Fair Value	2,865,202	428,431
Gross Unrealized Gains	27,633	26,735
Gross Unrealized Losses	(2,260)	(1,052)
Net Unrealized Gain/(Loss)	25,373	25,683
Non-Agency MBS | Expected to Recover Less Than Par
Schedule of MBS and CRT Securities [Line Items]
Principal/ Current Face	4,531,764	4,888,113
Purchase Premiums	0	0
Accretable Purchase Discounts	(332,014)	(370,063)
Discount Designated as Credit Reserve and OTTI	(847,017)	(900,557)
Amortized Cost	3,352,733	3,617,493
Fair Value	4,016,951	4,327,001
Gross Unrealized Gains	667,604	712,168
Gross Unrealized Losses	(3,386)	(2,660)
Net Unrealized Gain/(Loss)	$ 664,218	$ 709,508
Percentage of current face amount of Non-Agency MBS to be recovered	89.00%	83.00%
RPL/NPL MBS
Schedule of MBS and CRT Securities [Line Items]
Principal/ Current Face	$ 2,593,000	$ 161,000
Amortized Cost	2,590,000	161,000
Fair Value	2,592,000	161,000
RPL/NPL MBS | Linked Transactions
Schedule of MBS and CRT Securities [Line Items]
Par/Current Face		1,849,974
Amortized Cost		1,847,118
Fair Value		1,846,807
CRT securities
Schedule of MBS and CRT Securities [Line Items]
Principal/ Current Face	131,000	109,500
Purchase Premiums	0	0
Accretable Purchase Discounts	(4,411)	(4,727)
Discount Designated as Credit Reserve and OTTI	0	0
Amortized Cost	126,589	104,773
Fair Value	128,910	102,983
Gross Unrealized Gains	2,815	324
Gross Unrealized Losses	(494)	(2,114)
Net Unrealized Gain/(Loss)	$ 2,321	(1,790)
CRT securities | Linked Transactions
Schedule of MBS and CRT Securities [Line Items]
Par/Current Face		4,500
Amortized Cost		4,500
Fair Value		$ 4,624