MBS and CRT Securities (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2014 Security	Dec. 31, 2013	Dec. 31, 2012
Fair Value
Less than 12 months	$ 525,778,000
12 months or more	1,963,491,000
Total	2,489,269,000
Unrealized Losses
Less than 12 months	4,476,000
12 months or more	34,972,000
Total	39,448,000
Number of Securities
Less than 12 Months	64
12 Months or more	252
OTTI charges recorded
Total OTTI losses	0	0	(879,000)
OTTI (reclassified from)/recognized in other comprehensive income/(loss)	0	0	(321,000)
Net Impairment Losses Recognized in Earnings	0	0	(1,200,000)
Roll-forward of the credit loss component of OTTI
Credit loss component of OTTI at beginning of period	36,115,000	36,115,000	34,915,000
Additions for credit related OTTI not previously recognized	0	0	458,000
Subsequent additional credit related OTTI recorded	0	0	742,000
Credit loss component of OTTI at end of period	36,115,000	36,115,000	36,115,000
Significant inputs considered and assumptions made in determining the measurement of the component of OTTI recorded in earnings
Number of days considered to classify loans delinquent	60 days
Accumulated other comprehensive income from MBS and CRT securities:
Unrealized gain on MBS at beginning of period	752,912,000	824,808,000	55,491,000
Reclassification adjustment for MBS sales included in net income	(34,948,000)	(19,833,000)	(7,493,000)
Reclassification adjustment for OTTI included in net income	0	0	(1,200,000)
Change in AOCI from MBS and CRT securities	60,603,000	(71,896,000)	769,317,000
Balance at end of period	813,515,000	752,912,000	824,808,000
Low end of range
Significant inputs considered and assumptions made in determining the measurement of the component of OTTI recorded in earnings
Number of days considered to classify loans delinquent	60 days	60 days	60 days
Total MBS
Fair Value
Less than 12 months	456,418,000
12 months or more	1,963,491,000
Total	2,419,909,000
Unrealized Losses
Less than 12 months	2,362,000
12 months or more	34,972,000
Total	37,334,000
Number of Securities
Less than 12 Months	48
12 Months or more	252
Agency MBS
Fair Value
Less than 12 months	326,866,000
12 months or more	1,928,212,000
Total	2,255,078,000
Unrealized Losses
Less than 12 months	745,000
12 months or more	32,877,000
Total	33,622,000
Number of Securities
Less than 12 Months	32
12 Months or more	239
Accumulated other comprehensive income from MBS and CRT securities:
Unrealized (loss)/gain on MBS and CRT securities, net	65,739,000	(186,568,000)	(7,820,000)
MBS and CRT securities Interest Income
Coupon interest	189,355,000	213,995,000	248,048,000
Effective yield adjustment	(46,812,000)	(57,949,000)	(51,990,000)
Interest income	142,543,000	156,046,000	196,058,000
Agency MBS | Fannie Mae
Fair Value
Less than 12 months	309,631,000
12 months or more	1,260,461,000
Total	1,570,092,000
Unrealized Losses
Less than 12 months	735,000
12 months or more	20,365,000
Total	21,100,000
Number of Securities
Less than 12 Months	30
12 Months or more	139
Agency MBS | Freddie Mac
Fair Value
Less than 12 months	17,235,000
12 months or more	667,751,000
Total	684,986,000
Unrealized Losses
Less than 12 months	10,000
12 months or more	12,512,000
Total	12,522,000
Number of Securities
Less than 12 Months	2
12 Months or more	100
Non-Agency MBS
Fair Value
Less than 12 months	129,552,000
12 months or more	35,279,000
Total	164,831,000
Unrealized Losses
Less than 12 months	1,617,000
12 months or more	2,095,000
Total	3,712,000
Number of Securities
Less than 12 Months	16
12 Months or more	13
Credit-related OTTI losses	0	0	1,200,000
Significant inputs considered and assumptions made in determining the measurement of the component of OTTI recorded in earnings
Number of days considered to classify loans delinquent	60 days
Changes in the components of the purchase discount on Non-Agency MBS
Accretable purchase discount reallocated purchase discount designated as credit reserve	218,000
Purchase discount pertaining to linked transactions designated as accretable purchase discount reallocated to credit reserve		695,000
Accumulated other comprehensive income from MBS and CRT securities:
Unrealized (loss)/gain on MBS and CRT securities, net	31,602,000	134,505,000	785,830,000
Sales of MBS
Proceeds from Sale of Mortgage Backed Securities (MBS) categorized as Available-for-sale	123,900,000	152,600,000	168,900,000
Gain (Loss) on Sales of Mortgage Backed Securities (MBS)	37,500,000	25,800,000	9,000,000
MBS and CRT securities Interest Income
Coupon interest	212,971,000	253,581,000	265,018,000
Effective yield adjustment	103,359,000	73,189,000	37,954,000
Interest income	316,330,000	326,770,000	302,972,000
Non-Agency MBS | Discount Designated as Credit Reserve and OTTI
Changes in the components of the purchase discount on Non-Agency MBS
Balance at beginning of period	(1,043,037,000)	(1,380,506,000)
Accretion of discount	0	0
Realized credit losses	89,481,000	163,478,000
Purchases	(80,256,000)	(79,320,000)
Sales	44,692,000	45,371,000
Unlinking of Linked Transactions	(6,414,000)	0
Transfers/release of credit reserve	94,977,000	207,940,000
Balance at end of period	(900,557,000)	(1,043,037,000)
Non-Agency MBS | Accretable Discount
Changes in the components of the purchase discount on Non-Agency MBS
Balance at beginning of period	(460,039,000)	(371,626,000)
Accretion of discount	103,653,000	73,422,000
Realized credit losses	0	0
Purchases	30,003,000	32,152,000
Sales	20,360,000	13,953,000
Unlinking of Linked Transactions	1,436,000	0
Transfers/release of credit reserve	(94,977,000)	(207,940,000)
Balance at end of period	(399,564,000)	(460,039,000)
Non-Agency MBS | Weighted average
Significant inputs considered and assumptions made in determining the measurement of the component of OTTI recorded in earnings
Credit enhancement (as a percent)	0.00%	0.00%	3.26%
Projected CPR (as a percent)	0.00%	0.00%	9.90%
Projected Loss Severity (as a percent)	0.00%	0.00%	55.50%
60+ days delinquent (as a percent)	0.00%	0.00%	24.40%
Non-Agency MBS | Low end of range
Significant inputs considered and assumptions made in determining the measurement of the component of OTTI recorded in earnings
Credit enhancement (as a percent)	0.00%	0.00%	0.00%
Projected CPR (as a percent)	0.00%	0.00%	9.10%
Projected Loss Severity (as a percent)	0.00%	0.00%	45.90%
60+ days delinquent (as a percent)	0.00%	0.00%	18.20%
Non-Agency MBS | High end of range
Significant inputs considered and assumptions made in determining the measurement of the component of OTTI recorded in earnings
Credit enhancement (as a percent)	0.00%	0.00%	16.50%
Projected CPR (as a percent)	0.00%	0.00%	13.30%
Projected Loss Severity (as a percent)	0.00%	0.00%	60.00%
60+ days delinquent (as a percent)	0.00%	0.00%	32.40%
Non-Agency MBS | Expected to Recover Par
Fair Value
Less than 12 months	395,000
12 months or more	21,277,000
Total	21,672,000
Unrealized Losses
Less than 12 months	8,000
12 months or more	1,044,000
Total	1,052,000
Number of Securities
Less than 12 Months	1
12 Months or more	8
Non-Agency MBS | Expected to Recover Less Than Par
Fair Value
Less than 12 months	129,157,000
12 months or more	14,002,000
Total	143,159,000
Unrealized Losses
Less than 12 months	1,609,000
12 months or more	1,051,000
Total	2,660,000
Number of Securities
Less than 12 Months	15
12 Months or more	5
Non-Agency MBS and CRT securities
Unrealized Losses
Total	5,800,000
CRT securities
Fair Value
Less than 12 months	69,360,000
12 months or more	0
Total	69,360,000
Unrealized Losses
Less than 12 months	2,114,000
12 months or more	0
Total	2,114,000
Number of Securities
Less than 12 Months	16
12 Months or more	0
Accumulated other comprehensive income from MBS and CRT securities:
Unrealized (loss)/gain on MBS and CRT securities, net	(1,790,000)	0	0
MBS and CRT securities Interest Income
Coupon interest	665,000	0	0
Effective yield adjustment	107,000	0	0
Interest income	$ 772,000	$ 0	$ 0