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, 2012 Security	Sep. 30, 2011	Sep. 30, 2012 Security	Sep. 30, 2011	Sep. 30, 2012 Discount Designated as Credit Reserve and OTTI	Sep. 30, 2011 Discount Designated as Credit Reserve and OTTI	Sep. 30, 2012 Discount Designated as Credit Reserve and OTTI	Sep. 30, 2011 Discount Designated as Credit Reserve and OTTI	Sep. 30, 2012 Accretable Discount	Sep. 30, 2011 Accretable Discount	Sep. 30, 2012 Accretable Discount	Sep. 30, 2011 Accretable Discount	Sep. 30, 2012 Low end of range	Sep. 30, 2012 Low end of range	Sep. 30, 2012 Agency MBS Security	Sep. 30, 2011 Agency MBS	Sep. 30, 2012 Agency MBS Security	Sep. 30, 2011 Agency MBS	Sep. 30, 2012 Agency MBS Fannie Mae. Security	Dec. 31, 2011 Agency MBS Fannie Mae.	Sep. 30, 2012 Agency MBS Freddie Mac. Security	Dec. 31, 2011 Agency MBS Freddie Mac.	Sep. 30, 2012 Non-Agency MBS Security	Sep. 30, 2011 Non-Agency MBS	Sep. 30, 2012 Non-Agency MBS Security	Sep. 30, 2011 Non-Agency MBS	Sep. 30, 2011 Non-Agency MBS Weighted average	Sep. 30, 2012 Non-Agency MBS Weighted average	Sep. 30, 2011 Non-Agency MBS Weighted average	Sep. 30, 2011 Non-Agency MBS Low end of range	Sep. 30, 2012 Non-Agency MBS Low end of range	Sep. 30, 2011 Non-Agency MBS Low end of range	Sep. 30, 2011 Non-Agency MBS High end of range	Sep. 30, 2012 Non-Agency MBS High end of range	Sep. 30, 2011 Non-Agency MBS High end of range	Sep. 30, 2012 Non-Agency MBS Rated AAA	Dec. 31, 2011 Non-Agency MBS Rated AAA	Sep. 30, 2012 Non-Agency MBS Rated AA Security	Dec. 31, 2011 Non-Agency MBS Rated AA	Sep. 30, 2012 Non-Agency MBS Rated A Security	Dec. 31, 2011 Non-Agency MBS Rated A	Sep. 30, 2012 Non-Agency MBS Rated BBB Security	Dec. 31, 2011 Non-Agency MBS Rated BBB	Sep. 30, 2012 Non-Agency MBS Rated BB Security	Dec. 31, 2011 Non-Agency MBS Rated BB	Sep. 30, 2012 Non-Agency MBS Rated B Security	Dec. 31, 2011 Non-Agency MBS Rated B	Sep. 30, 2012 Non-Agency MBS Rated CCC Security	Dec. 31, 2011 Non-Agency MBS Rated CCC	Sep. 30, 2012 Non-Agency MBS Rated CC Security	Dec. 31, 2011 Non-Agency MBS Rated CC	Sep. 30, 2012 Non-Agency MBS Rated C Security	Dec. 31, 2011 Non-Agency MBS Rated C	Sep. 30, 2012 Non-Agency MBS Unrated and other Security	Dec. 31, 2011 Non-Agency MBS Unrated and other
Fair Value
Less than 12 months	$ 124,316,000		$ 124,316,000												$ 117,361,000		$ 117,361,000		$ 117,361,000				$ 6,955,000		$ 6,955,000																							$ 6,955,000
12 months or more	531,581,000		531,581,000												48,133,000		48,133,000		45,376,000		2,757,000		483,448,000		483,448,000													39,000		22,214,000		1,282,000		30,000,000		97,342,000		72,474,000		48,847,000		74,379,000		136,871,000
Total	655,897,000		655,897,000												165,494,000		165,494,000		162,737,000		2,757,000		490,403,000		490,403,000													39,000		22,214,000		1,282,000		30,000,000		97,342,000		79,429,000		48,847,000		74,379,000		136,871,000
Unrealized Losses
Less than 12 months	232,000		232,000												214,000		214,000		214,000				18,000		18,000																							18,000
12 months or more	13,934,000		13,934,000												747,000		747,000		735,000		12,000		13,187,000		13,187,000													8,000		1,143,000		167,000		1,053,000		2,243,000		3,337,000		672,000		1,677,000		2,887,000
Total	14,166,000		14,166,000												961,000		961,000		949,000		12,000		13,205,000		13,205,000													8,000		1,143,000		167,000		1,053,000		2,243,000		3,355,000		672,000		1,677,000		2,887,000
Number of Securities
Less than 12 months (in security)	24		24												23		23		23				1		1																							1
12 months or more (in security)	61		61												11		11		10		1		50		50													1		2		2		5		8		8		5		5		14
Credit-related OTTI losses recognized during the period		3,991,000	1,200,000	6,383,000																				4,000,000	1,200,000	6,400,000
OTTI charges recorded
Total OTTI losses		(14,913,000)	(879,000)	(15,550,000)
OTTI recognized in/(reclassified from) other comprehensive income		10,922,000	(321,000)	9,167,000
OTTI recognized in earnings		(3,991,000)	(1,200,000)	(6,383,000)																				(4,000,000)	(1,200,000)	(6,400,000)
Roll-forward of the credit loss component of OTTI
Credit loss component of OTTI at beginning of period	36,115,000		34,915,000
Additions for credit related OTTI not previously recognized			458,000
Subsequent additional credit related OTTI recorded			742,000
Credit loss component of OTTI at end of period	36,115,000		36,115,000
Significant inputs considered and assumptions made in determining the measurement of the component of OTTI recorded in earnings
Credit enhancement (as a percent)																											2.70%	3.26%	3.02%	0.00%	0.00%	0.00%	10.40%	16.50%	13.30%
Projected CPR (as a percent)																											11.00%	9.90%	10.90%	6.90%	9.10%	1.90%	12.20%	13.30%	12.20%
Projected Loss Severity (as a percent)																											56.10%	55.50%	53.60%	46.10%	45.90%	41.90%	70.00%	60.00%	70.00%
60+ days delinquent (as a percent)																											21.40%	24.40%	21.30%	9.10%	18.20%	7.30%	36.70%	32.40%	36.70%
Number of days considered to classify loans delinquent													60 days	60 days
Changes in the components of the purchase discount on Non-Agency MBS
Balance at beginning of period					(1,440,752,000)	(1,174,890,000)	(1,228,766,000)	(746,678,000)	(265,137,000)	(222,930,000)	(250,479,000)	(228,966,000)
Accretion of discount									8,816,000	10,785,000	28,107,000	33,107,000
Realized credit losses					49,314,000	10,735,000	107,229,000	20,612,000
Purchases					(122,266,000)	(29,141,000)	(370,649,000)	(360,655,000)	4,554,000	(16,198,000)	(3,883,000)	(19,035,000)
Reclassification adjustment for OTTI							866,000	101,000			(866,000)	(101,000)
Net impairment losses recognized in earnings						(3,991,000)	(1,200,000)	(6,383,000)
Unlinking of Linked Transactions						(10,419,000)	(38,662,000)	(116,489,000)	(2,256,000)	(61,000)	(9,424,000)	(11,623,000)
Transfers/release of credit reserve					54,053,000	11,305,000	71,531,000	13,091,000	(54,053,000)	(11,305,000)	(71,531,000)	(13,091,000)
Balance at end of period					(1,459,651,000)	(1,196,401,000)	(1,459,651,000)	(1,196,401,000)	(308,076,000)	(239,709,000)	(308,076,000)	(239,709,000)
Accumulated other comprehensive income from MBS:
Balance at the beginning of the period	296,007,000	292,376,000	55,491,000	393,822,000													216,256,000		230,940,000	193,417,000	26,436,000	22,513,000			(160,765,000)											1,110,000	(245,000)	(8,000)	(14,000)	(1,143,000)	(4,175,000)	1,814,000	(4,681,000)	1,403,000	(4,785,000)	14,793,000	(22,921,000)	104,254,000	(19,020,000)	42,251,000	(23,790,000)	81,398,000	(72,822,000)	260,850,000	(8,312,000)
Unrealized gain on Agency MBS, net	61,999,000	12,035,000	47,169,000	50,092,000
Unrealized gain/(loss) on Non-Agency MBS, net	409,742,000	(109,294,000)	666,287,000	(250,845,000)
Reclassification adjustment for MBS sales included in net income	(3,130,000)	(4,525,000)	(5,529,000)	(4,869,000)
Reclassification adjustment for OTTI included in net income		3,991,000	1,200,000	6,383,000
Change in accumulated other comprehensive income/(loss) from MBS	468,611,000	(97,793,000)	709,127,000	(199,239,000)
Balance at the end of period	764,618,000	194,583,000	764,618,000	194,583,000											257,896,000		257,896,000		230,940,000	193,417,000	26,436,000	22,513,000	506,722,000		506,722,000											1,110,000	(245,000)	(8,000)	(14,000)	(1,143,000)	(4,175,000)	1,814,000	(4,681,000)	1,403,000	(4,785,000)	14,793,000	(22,921,000)	104,254,000	(19,020,000)	42,251,000	(23,790,000)	81,398,000	(72,822,000)	260,850,000	(8,312,000)
Purchase discount pertaining to linked transactions designated as accretable purchase discount reallocated to credit reserve																							54,000	1,100,000	575,000	309,000
Sales of MBS
Amount of MBS sold															66,000,000		137,100,000	76,500,000
Gross gains on sale of MBS															4,300,000		7,200,000	4,200,000
MBS Interest Income
Coupon interest															61,978,000	70,654,000	187,963,000	212,703,000					69,139,000	60,038,000	196,144,000	153,563,000
Effective yield adjustment															(14,780,000)	(10,697,000)	(37,915,000)	(26,589,000)					8,760,000	10,746,000	27,913,000	32,970,000
Interest on mortgage backed securities															$ 47,198,000	$ 59,957,000	$ 150,048,000	$ 186,114,000					$ 77,899,000	$ 70,784,000	$ 224,057,000	$ 186,533,000