MBS (Details 2) (USD $)	3 Months Ended					12 Months Ended														12 Months Ended			9 Months Ended	12 Months Ended		9 Months Ended	12 Months Ended		9 Months Ended	12 Months Ended
	Dec. 31, 2011 Security	Sep. 30, 2011	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010	Dec. 31, 2011 D Security	Dec. 31, 2010 D	Dec. 31, 2009 D	Dec. 31, 2011 Discount Designated as Credit Reserve and OTTI	Dec. 31, 2010 Discount Designated as Credit Reserve and OTTI	Dec. 31, 2011 Accretable Discount	Dec. 31, 2010 Accretable Discount	Dec. 31, 2011 Agency MBS Security	Dec. 31, 2010 Agency MBS	Dec. 31, 2009 Agency MBS	Dec. 31, 2011 Agency MBS Fannie Mae. Security	Dec. 31, 2010 Agency MBS Fannie Mae.	Dec. 31, 2011 Agency MBS Freddie Mac. Security	Dec. 31, 2010 Agency MBS Freddie Mac.	Dec. 31, 2011 Non-Agency MBS Security	Dec. 31, 2010 Non-Agency MBS NonAgencyMBS Security	Dec. 31, 2009 Non-Agency MBS	Dec. 31, 2009 Non-Agency MBS Weighted average	Dec. 31, 2011 Non-Agency MBS Weighted average	Dec. 31, 2010 Non-Agency MBS Weighted average	Dec. 31, 2009 Non-Agency MBS Low end of range	Dec. 31, 2011 Non-Agency MBS Low end of range	Dec. 31, 2010 Non-Agency MBS Low end of range	Dec. 31, 2009 Non-Agency MBS High end of range	Dec. 31, 2011 Non-Agency MBS High end of range	Dec. 31, 2010 Non-Agency MBS High end of range	Dec. 31, 2011 Non-Agency MBS Rated AAA Security	Dec. 31, 2010 Non-Agency MBS Rated AAA	Dec. 31, 2011 Non-Agency MBS Rated AA Security	Dec. 31, 2010 Non-Agency MBS Rated AA	Dec. 31, 2011 Non-Agency MBS Rated A Security	Dec. 31, 2010 Non-Agency MBS Rated A	Dec. 31, 2011 Non-Agency MBS Rated BBB Security	Dec. 31, 2010 Non-Agency MBS Rated BBB	Dec. 31, 2011 Non-Agency MBS Rated BB Security	Dec. 31, 2010 Non-Agency MBS Rated BB	Dec. 31, 2011 Non-Agency MBS Rated B Security	Dec. 31, 2010 Non-Agency MBS Rated B	Dec. 31, 2011 Non-Agency MBS Rated CCC Security	Dec. 31, 2010 Non-Agency MBS Rated CCC	Dec. 31, 2011 Non-Agency MBS Rated CC Security	Dec. 31, 2010 Non-Agency MBS Rated CC	Dec. 31, 2011 Non-Agency MBS Rated C Security	Dec. 31, 2010 Non-Agency MBS Rated C	Dec. 31, 2011 Non-Agency MBS Unrated and other Security	Dec. 31, 2010 Non-Agency MBS Unrated and other
Fair Value
Less than 12 months	$ 2,808,792,000					$ 2,808,792,000							$ 147,900,000			$ 127,538,000		$ 20,362,000		$ 2,660,892,000												$ 12,258,000						$ 36,943,000		$ 59,686,000		$ 230,868,000		$ 526,777,000		$ 309,112,000		$ 1,139,608,000		$ 345,640,000
12 months or more	357,961,000					357,961,000							139,913,000			136,951,000		2,962,000		218,048,000														35,000		23,280,000		1,409,000		9,820,000		13,567,000		16,610,000		32,400,000		85,734,000		35,193,000
Total	3,166,753,000					3,166,753,000							287,813,000			264,489,000		23,324,000		2,878,940,000												12,258,000		35,000		23,280,000		38,352,000		69,506,000		244,435,000		543,387,000		341,512,000		1,225,342,000		380,833,000
Unrealized Losses
Less than 12 months	254,458,000					254,458,000							671,000			525,000		146,000		253,787,000												245,000						4,196,000		5,810,000		23,035,000		42,072,000		34,374,000		106,696,000		37,359,000
12 months or more	35,251,000					35,251,000							1,073,000			1,055,000		18,000		34,178,000														14,000		4,516,000		485,000		1,207,000		2,615,000		4,715,000		3,625,000		11,114,000		5,887,000
Total	289,709,000					289,709,000							1,744,000			1,580,000		164,000		287,965,000												245,000		14,000		4,516,000		4,681,000		7,017,000		25,650,000		46,787,000		37,999,000		117,810,000		43,246,000
Number of Securities
Less than 12 months	241					241							22			20		2		219												1						6		7		16		45		23		84		37
12 months or more	41					41							18			17		1		23														1		3		2		2		2		3		4		3		3
Number of securities held with recognized credit-related OTTI losses																				35
Credit-related OTTI losses recognized during the period	4,187,000	3,991,000	2,392,000	6,865,000	5,412,000	10,570,000	12,277,000	17,928,000												10,600,000	12,300,000
Number of non-agency MBS																					8
OTTI charges recorded
Total OTTI losses						45,144,000	6,042,000	85,110,000
OTTI recognized in (reclassified from) classified from other comprehensive income/(loss)						(34,574,000)	6,235,000	(67,182,000)
OTTI recognized in earnings	4,187,000	3,991,000	2,392,000	6,865,000	5,412,000	10,570,000	12,277,000	17,928,000												10,600,000	12,300,000
Roll-forward of the credit loss component of OTTI
Credit loss component of OTTI at beginning of period						24,345,000	17,928,000	1,549,000
Additions for credit related OTTI not previously recognized						7,158,000		9,540,000
Subsequent additional credit related OTTI recorded						3,412,000	6,417,000	6,839,000
Credit loss component of OTTI at end of period	34,915,000			24,345,000		34,915,000	24,345,000	17,928,000
Significant inputs considered and assumptions made in determining the measurement of the component of OTTI recorded in earnings
Credit enhancement																							6.54%	2.90%	6.30%	0.00%	0.00%	0.00%	18.32%	13.30%	23.11%
Projected CPR																							11.29%	10.70%	11.22%	5.97%	1.90%	5.19%	16.37%	13.80%	19.85%
Projected Loss Severity																							48.55%	52.10%	51.48%	45.00%	41.90%	45.00%	60.00%	70.00%	62.00%
60+ days delinquent																							18.13%	22.60%	20.56%	13.06%	7.30%	5.46%	21.63%	36.70%	36.76%
Minimum number of days considered to classify loans delinquent						60	60	60
Accumulated other comprehensive income from MBS:
Balance at the beginning of the period						393,822,000	339,470,000	(72,983,000)					162,607,000			193,417,000	151,955,000	22,513,000	10,227,000	231,215,000												(245,000)	(215,000)	(14,000)	(2,911,000)	(4,175,000)	4,237,000	(4,681,000)	(1,703,000)	(4,785,000)	4,057,000	(22,921,000)	9,705,000	(19,020,000)	62,866,000	(23,790,000)	62,895,000	(72,822,000)	82,043,000	(8,312,000)	10,241,000
Unrealized gain/(loss) on Agency MBS, net						61,149,000	(59,644,000)	210,774,000
Unrealized (loss)/gain on Non-Agency MBS, net						(381,410,000)	167,732,000	222,959,000
Reclassification adjustment for MBS sales included in net income						(7,500,000)	(41,459,000)	(3,352,000)
Reclassification adjustment for OTTI included in net income						(10,570,000)	(12,277,000)	(17,928,000)
Balance at the end of period	55,491,000			393,822,000		55,491,000	393,822,000	339,470,000					216,256,000	162,607,000		193,417,000	151,955,000	22,513,000	10,227,000	(160,765,000)	231,215,000											(245,000)	(215,000)	(14,000)	(2,911,000)	(4,175,000)	4,237,000	(4,681,000)	(1,703,000)	(4,785,000)	4,057,000	(22,921,000)	9,705,000	(19,020,000)	62,866,000	(23,790,000)	62,895,000	(72,822,000)	82,043,000	(8,312,000)	10,241,000
Changes in the components of the purchase discount on Non-Agency MBS
Balance at beginning of period									(746,678,000)	(472,710,000)	(228,966,000)	(149,319,000)
Accretion of discount											42,358,000	34,759,000
Realized credit losses									33,074,000	5,144,000
Purchases									(402,093,000)	(329,551,000)	(23,440,000)	(23,162,000)
Sales										7,856,000		683,000
Reclassification adjustment for OTTI									101,000	(410,000)	(101,000)	410,000
Net impairment losses recognized in earnings									(10,570,000)	(12,277,000)
Unlinking of Linked Transactions									(127,102,000)	(32,086,000)	(15,828,000)	(4,981,000)
Transfers/release of credit reserve									24,502,000	87,356,000	(24,502,000)	(87,356,000)
Balance at end of period									(1,228,766,000)	(746,678,000)	(250,479,000)	(228,966,000)
Purchase discount pertaining to linked transactions designated as accretable purchase discount reallocated to credit reserve																				20,000
Purchase discount pertaining to linked transactions designated as credit reserve reallocated to accretable purchase discount																					19,300,000
Sales of MBS
Amount of MBS sold													150,600,000	931,900,000	650,900,000						7,200,000
Gross gains on sale of MBS													6,700,000	33,100,000	22,600,000						654,000
Number of MBS sold																					1
MBS Interest Income
Coupon interest													280,206,000	291,138,000	464,260,000					212,452,000	105,592,000	46,772,000
Effective yield adjustment													(38,212,000)	(40,536,000)	(23,903,000)					42,165,000	34,759,000	17,335,000
Interest on mortgage backed securities													$ 241,994,000	$ 250,602,000	$ 440,357,000					$ 254,617,000	$ 140,351,000	$ 64,107,000