MBS (Details 2) (USD $)	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended						3 Months Ended		9 Months Ended																					3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2011 D Unit Security Counterparty Y	Sep. 30, 2010	Sep. 30, 2011 M D Component Lease Unit Security Counterparty Y	Sep. 30, 2010	Sep. 30, 2011 Agency MBS Security	Sep. 30, 2010 Agency MBS	Sep. 30, 2011 Agency MBS Security	Sep. 30, 2010 Agency MBS	Sep. 30, 2011 Agency MBS Fannie Mae. Security	Dec. 31, 2010 Agency MBS Fannie Mae.	Sep. 30, 2011 Agency MBS Freddie Mac. Security	Dec. 31, 2010 Agency MBS Freddie Mac.	Sep. 30, 2011 Non-Agency MBS Security	Sep. 30, 2010 Non-Agency MBS Security	Sep. 30, 2011 Non-Agency MBS Security	Sep. 30, 2010 Non-Agency MBS	Dec. 31, 2010 Non-Agency MBS Rated AAA	Sep. 30, 2011 Non-Agency MBS Rated AA Security	Dec. 31, 2010 Non-Agency MBS Rated AA	Sep. 30, 2011 Non-Agency MBS Rated A Security	Dec. 31, 2010 Non-Agency MBS Rated A	Sep. 30, 2011 Non-Agency MBS Rated BBB Security	Dec. 31, 2010 Non-Agency MBS Rated BBB	Sep. 30, 2011 Non-Agency MBS Rated BB Security	Dec. 31, 2010 Non-Agency MBS Rated BB	Sep. 30, 2011 Non-Agency MBS Rated B Security	Dec. 31, 2010 Non-Agency MBS Rated B	Sep. 30, 2011 Non-Agency MBS Rated CCC Security	Dec. 31, 2010 Non-Agency MBS Rated CCC	Sep. 30, 2011 Non-Agency MBS Rated CC Security	Dec. 31, 2010 Non-Agency MBS Rated CC	Sep. 30, 2011 Non-Agency MBS Rated C Security	Dec. 31, 2010 Non-Agency MBS Rated C	Sep. 30, 2011 Non-Agency MBS Unrated and other Security	Dec. 31, 2010 Non-Agency MBS Unrated and other	Sep. 30, 2011 Non-Agency MBS Credit enhancement	Sep. 30, 2011 Non-Agency MBS Credit enhancement	Sep. 30, 2011 Non-Agency MBS Projected CPR	Sep. 30, 2011 Non-Agency MBS Projected CPR	Sep. 30, 2011 Non-Agency MBS Projected Loss Severity	Sep. 30, 2011 Non-Agency MBS Projected Loss Severity	Sep. 30, 2011 Non-Agency MBS 60+ days delinquent	Sep. 30, 2011 Non-Agency MBS 60+ days delinquent	Sep. 30, 2011 Discount Designated as Credit Reserve and OTTI	Sep. 30, 2010 Discount Designated as Credit Reserve and OTTI	Sep. 30, 2011 Discount Designated as Credit Reserve and OTTI	Sep. 30, 2010 Discount Designated as Credit Reserve and OTTI	Sep. 30, 2011 Accretable Discount	Sep. 30, 2010 Accretable Discount	Sep. 30, 2011 Accretable Discount	Sep. 30, 2010 Accretable Discount
Fair Value
Less than 12 months	$ 3,177,987,000		$ 3,177,987,000		$ 557,982,000		$ 557,982,000		$ 535,456,000		$ 22,526,000		$ 2,620,005,000		$ 2,620,005,000					$ 2,842,000		$ 36,422,000		$ 62,485,000		$ 245,293,000		$ 600,747,000		$ 727,495,000		$ 653,817,000		$ 290,904,000
12 months or more	330,069,000		330,069,000		157,720,000		157,720,000		154,717,000		3,003,000		172,349,000		172,349,000			35,000		24,933,000		1,499,000		10,270,000		14,392,000		18,012,000		3,516,000		81,490,000		18,202,000
Total	3,508,056,000		3,508,056,000		715,702,000		715,702,000		690,173,000		25,529,000		2,792,354,000		2,792,354,000			35,000		27,775,000		37,921,000		72,755,000		259,685,000		618,759,000		731,011,000		735,307,000		309,106,000
Unrealized Losses
Less than 12 months	159,013,000		159,013,000		1,689,000		1,689,000		1,572,000		117,000		157,324,000		157,324,000					282,000		2,509,000		3,957,000		15,497,000		31,975,000		51,424,000		36,562,000		15,118,000
12 months or more	24,724,000		24,724,000		1,837,000		1,837,000		1,776,000		61,000		22,887,000		22,887,000			14,000		4,000,000		423,000		1,022,000		2,236,000		4,003,000		542,000		6,547,000		4,100,000
Total	183,737,000		183,737,000		3,526,000		3,526,000		3,348,000		178,000		180,211,000		180,211,000			14,000		4,282,000		2,932,000		4,979,000		17,733,000		35,978,000		51,966,000		43,109,000		19,218,000
Number of Securities
Less than 12 months	242		242		41		41		39		2		201		201					1		5		7		17		48		50		50		23
12 months or more	38		38		19		19		18		1		19		19			1		3		2		2		2		3		2		2		2
Number of securities held with recognized credit-related OTTI losses													14	6	20
Credit-related OTTI losses recognized during the period	3,991,000		6,383,000	5,412,000									4,000,000		6,400,000	5,400,000
OTTI charges recorded
OTTI included in earnings	3,991,000		6,383,000	5,412,000									4,000,000		6,400,000	5,400,000
OTTI recognized in (reclassified from) classified from other comprehensive	10,922,000		9,167,000	(5,228,000)
Total OTTI losses	14,913,000		15,550,000	184,000
Roll-forward of the credit loss component of OTTI
Credit loss component of OTTI at beginning of period	26,739,000		24,347,000
Additions for credit related OTTI not previously recognized	3,991,000		3,991,000
Subsequent additional credit related OTTI recorded			2,392,000
Credit loss component of OTTI at end of period	30,730,000		30,730,000
Significant inputs considered and assumptions made in determining the measurement of the component of OTTI recorded in earnings
Weighted average (as a percent)																																				2.70%	3.02%	11.00%	10.90%	56.10%	53.60%	21.40%	21.30%
Low end of range (as a percent)																																				0.00%	0.00%	6.90%	1.90%	46.10%	41.90%	9.10%	7.30%
High end of range (as a percent)																																				10.40%	13.30%	12.20%	12.20%	70.00%	70.00%	36.70%	36.70%
Minimum number of days considered to classify loans delinquent	60		60
Accumulated other comprehensive income from MBS:
Balance at the beginning of the period	292,376,000	353,457,000	393,822,000	339,470,000			162,607,000		183,200,000	151,955,000	24,269,000	10,227,000			231,215,000		(215,000)	(14,000)	(2,911,000)	(3,883,000)	4,237,000	(677,000)	(1,703,000)	(4,768,000)	4,057,000	(9,846,000)	9,705,000	7,436,000	62,866,000	(19,113,000)	62,895,000	1,557,000	82,043,000	16,061,000	10,241,000
Unrealized gain on Agency MBS, net	12,035,000	5,899,000	50,092,000	(1,465,000)
Unrealized loss on Non-Agency MBS, net	(109,294,000)	42,162,000	(250,845,000)	99,560,000
Reclassification adjustment for MBS sales included in net income	(4,525,000)		(4,869,000)	(41,459,000)
Reclassification adjustment for OTTI included in net income	3,991,000		6,383,000	5,412,000
Balance at the end of period	194,583,000	401,518,000	194,583,000	401,518,000	207,830,000		207,830,000		183,200,000	151,955,000	24,269,000	10,227,000	(13,247,000)		(13,247,000)		(215,000)	(14,000)	(2,911,000)	(3,883,000)	4,237,000	(677,000)	(1,703,000)	(4,768,000)	4,057,000	(9,846,000)	9,705,000	7,436,000	62,866,000	(19,113,000)	62,895,000	1,557,000	82,043,000	16,061,000	10,241,000
Changes in the components of the purchase discount on Non-Agency MBS
Balance at beginning of period																																												(1,174,890,000)	(604,785,000)	(746,678,000)	(472,710,000)	(222,930,000)	(208,938,000)	(228,966,000)	(149,319,000)
Accretion of discount																																																10,785,000	9,355,000	33,107,000	27,138,000
Realized credit losses																																												10,735,000	2,019,000	20,612,000	3,153,000
Purchases																																												(29,141,000)	(67,547,000)	(360,655,000)	(266,593,000)	(16,198,000)	(10,694,000)	(19,035,000)	(19,483,000)
Sales																																															7,856,000				683,000
Reclassification adjustment for OTTI																																														101,000	520,000			(101,000)	(520,000)
Net impairment losses recognized in earnings																																												(3,991,000)		(6,383,000)	(5,412,000)
Unlinking of Linked Transactions																																												(10,419,000)	(23,639,000)	(116,489,000)	(26,379,000)	(61,000)	241,000	(11,623,000)	(2,922,000)
Transfers/release of credit reserve																																												11,305,000	5,145,000	13,091,000	70,758,000	(11,305,000)	(5,145,000)	(13,091,000)	(70,758,000)
Balance at end of period																																												(1,196,401,000)	(688,807,000)	(1,196,401,000)	(688,807,000)	(239,709,000)	(215,181,000)	(239,709,000)	(215,181,000)
Purchase discount pertaining to linked transactions designated as accretable purchase discount reallocated to credit reserve													1,300,000		474,000
Purchase discount pertaining to linked transactions designated as credit reserve reallocated to accretable purchase discount														1,100,000		18,300,000
Sales of MBS
Amount of MBS sold							76,500,000	931,900,000								7,200,000
Gross gains on sale of MBS							4,200,000	33,100,000								654,000
Number of MBS sold							7									1
MBS Interest Income
Coupon interest					70,654,000	68,887,000	212,703,000	226,010,000					60,038,000	27,605,000	153,563,000	72,849,000
Effective yield adjustment					(10,697,000)	(8,497,000)	(26,589,000)	(32,412,000)					10,746,000	9,301,000	32,970,000	27,008,000
Interest on mortgage backed securities					$ 59,957,000	$ 60,390,000	$ 186,114,000	$ 193,598,000					$ 70,784,000	$ 36,906,000	$ 186,533,000	$ 99,857,000