MBS (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2014		Dec. 31, 2013
Information about MBS
Minimum term of fixed rate mortgages underlying MBS	15 years
Principal/ Current Face	$ 12,299,015,000		$ 11,892,957,000
Purchase Premiums	250,581,000		227,533,000
Accretable Purchase Discounts	(442,239,000)		(460,126,000)
Discount Designated as Credit Reserve and OTTI	(1,041,933,000)	[1]	(1,043,037,000)	[1]
Amortized Cost	11,066,966,000	[2]	10,618,446,000	[2]
Fair Value	11,886,188,000		11,371,358,000
Gross Unrealized Gains	897,640,000		848,946,000
Gross Unrealized Losses	(78,418,000)		(96,034,000)
Net Unrealized Gain/(Loss)	819,222,000		752,912,000
Principal payments receivable	1,500,000		1,100,000
Agency MBS
Information about MBS
Principal/ Current Face	6,557,372,000		6,276,919,000
Purchase Premiums	249,984,000		226,895,000
Accretable Purchase Discounts	(83,000)		(87,000)
Discount Designated as Credit Reserve and OTTI	0	[1]	0	[1]
Amortized Cost	6,808,815,000	[2]	6,504,846,000	[2]
Fair Value	6,841,033,000		6,519,221,000
Gross Unrealized Gains	107,863,000		106,660,000
Gross Unrealized Losses	(75,645,000)		(92,285,000)
Net Unrealized Gain/(Loss)	32,218,000		14,375,000
Agency MBS | Fannie Mae.
Information about MBS
Principal/ Current Face	5,411,010,000		5,092,410,000
Purchase Premiums	206,174,000		181,710,000
Accretable Purchase Discounts	(83,000)		(87,000)
Discount Designated as Credit Reserve and OTTI	0	[1]	0	[1]
Amortized Cost	5,617,101,000	[2]	5,274,033,000	[2]
Fair Value	5,666,693,000		5,315,363,000
Gross Unrealized Gains	96,973,000		96,516,000
Gross Unrealized Losses	(47,381,000)		(55,186,000)
Net Unrealized Gain/(Loss)	49,592,000		41,330,000
Agency MBS | Freddie Mac.
Information about MBS
Principal/ Current Face	1,133,983,000		1,171,841,000
Purchase Premiums	43,598,000		44,967,000
Accretable Purchase Discounts	0		0
Discount Designated as Credit Reserve and OTTI	0	[1]	0	[1]
Amortized Cost	1,179,123,000	[2]	1,217,927,000	[2]
Fair Value	1,161,428,000		1,190,670,000
Gross Unrealized Gains	10,569,000		9,842,000
Gross Unrealized Losses	(28,264,000)		(37,099,000)
Net Unrealized Gain/(Loss)	(17,695,000)		(27,257,000)
Agency MBS | Ginnie Mae.
Information about MBS
Principal/ Current Face	12,379,000		12,668,000
Purchase Premiums	212,000		218,000
Accretable Purchase Discounts	0		0
Discount Designated as Credit Reserve and OTTI	0	[1]	0	[1]
Amortized Cost	12,591,000	[2]	12,886,000	[2]
Fair Value	12,912,000		13,188,000
Gross Unrealized Gains	321,000		302,000
Gross Unrealized Losses	0		0
Net Unrealized Gain/(Loss)	321,000		302,000
Non-Agency MBS
Information about MBS
Principal/ Current Face	5,741,643,000		5,616,038,000
Purchase Premiums	597,000		638,000
Accretable Purchase Discounts	(442,156,000)		(460,039,000)
Discount Designated as Credit Reserve and OTTI	(1,041,933,000)	[1]	(1,043,037,000)	[1]
Amortized Cost	4,258,151,000	[2]	4,113,600,000	[2]
Fair Value	5,045,155,000		4,852,137,000
Gross Unrealized Gains	789,777,000		742,286,000
Gross Unrealized Losses	(2,773,000)		(3,749,000)
Net Unrealized Gain/(Loss)	787,004,000		738,537,000
Credit Reserve	997,600,000		998,500,000
OTTI	44,400,000		44,500,000
Non-Agency MBS Expected to Recover Par | Non-Agency MBS
Information about MBS
Principal/ Current Face	239,898,000	[3]	234,187,000	[3]
Purchase Premiums	597,000	[3]	638,000	[3]
Accretable Purchase Discounts	(24,442,000)	[3]	(24,450,000)	[3]
Discount Designated as Credit Reserve and OTTI	0	[1],[3]	0	[1],[3]
Amortized Cost	216,053,000	[2],[3]	210,375,000	[2],[3]
Fair Value	237,590,000	[3]	230,738,000	[3]
Gross Unrealized Gains	22,748,000	[3]	21,720,000	[3]
Gross Unrealized Losses	(1,211,000)	[3]	(1,357,000)	[3]
Net Unrealized Gain/(Loss)	21,537,000	[3]	20,363,000	[3]
Non-Agency MBS Expected to Recover Less Than Par | Non-Agency MBS
Information about MBS
Principal/ Current Face	5,501,745,000	[3],[4]	5,381,851,000	[3],[4]
Purchase Premiums	0	[3],[4]	0	[3],[4]
Accretable Purchase Discounts	(417,714,000)	[3],[4]	(435,589,000)	[3],[4]
Discount Designated as Credit Reserve and OTTI	(1,041,933,000)	[1],[3],[4]	(1,043,037,000)	[1],[3],[4]
Amortized Cost	4,042,098,000	[2],[3],[4]	3,903,225,000	[2],[3],[4]
Fair Value	4,807,565,000	[3],[4]	4,621,399,000	[3],[4]
Gross Unrealized Gains	767,029,000	[3],[4]	720,566,000	[3],[4]
Gross Unrealized Losses	(1,562,000)	[3],[4]	(2,392,000)	[3],[4]
Net Unrealized Gain/(Loss)	$ 765,467,000	[3],[4]	$ 718,174,000	[3],[4]
Percentage of Current Face Amount of Non-Agency MBS to be Recovered	81.00%		81.00%

[1] Discount designated as Credit Reserve and amounts related to OTTI are generally not expected to be accreted into interest income. Amounts disclosed at March 31, 2014 reflect Credit Reserve of $997.6 million and OTTI of $44.4 million. Amounts disclosed at December 31, 2013 reflect Credit Reserve of $998.5 million and OTTI of $44.5 million.

[2] Includes principal payments receivable of $1.5 million and $1.1 million at March 31, 2014 and December 31, 2013, respectively, which are not included in the Principal/Current Face.

[3] Based on management’s current estimates of future principal cash flows expected to be received.

[4] At March 31, 2014 and December 31, 2013, the Company expected to recover approximately 81% of the then-current face amount of Non-Agency MBS.