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Schedule of Mortgage-Backed Securities by Weighted Average Life (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Mortgage-Backed Securities [Line Items]
Mortgage-backed securities, at fair value	$ 1,630,575	$ 1,685,998
Non-Agency RMBS [Member]
Mortgage-Backed Securities [Line Items]
Mortgage-backed securities, at fair value	12,442	18,025
Amortized Cost	$ 10,503	$ 15,278
Weighted Average Coupon Rate, Percent	3.94%	3.58%
Less than three years [Member] | Non-Agency RMBS [Member]
Mortgage-Backed Securities [Line Items]
Mortgage-backed securities, at fair value	$ 0	$ 0
Amortized Cost	$ 0	$ 0
Weighted Average Coupon Rate, Percent	0.00%	0.00%
Greater than three years and less than seven years [Member] | Non-Agency RMBS [Member]
Mortgage-Backed Securities [Line Items]
Mortgage-backed securities, at fair value	$ 7,784	$ 9,625
Amortized Cost	$ 6,861	$ 9,062
Weighted Average Coupon Rate, Percent	4.89%	5.00%
Greater than seven years and less than eleven years [Member] | Non-Agency RMBS [Member]
Mortgage-Backed Securities [Line Items]
Mortgage-backed securities, at fair value	$ 2,188	$ 5,892
Amortized Cost	$ 1,111	$ 3,697
Weighted Average Coupon Rate, Percent	2.89%	2.14%
Greater than eleven years [Member] | Non-Agency RMBS [Member]
Mortgage-Backed Securities [Line Items]
Mortgage-backed securities, at fair value	$ 2,470	$ 2,508
Amortized Cost	$ 2,531	$ 2,519
Weighted Average Coupon Rate, Percent	2.50%	2.18%
Fixed Rate [Member] | Agency RMBS [Member]
Mortgage-Backed Securities [Line Items]
Mortgage-backed securities, at fair value	$ 1,603,607	$ 1,655,768
Amortized Cost	$ 1,643,485	$ 1,669,060
Weighted Average Coupon Rate, Percent	3.90%	3.92%
Fixed Rate [Member] | Less than three years [Member] | Agency RMBS [Member]
Mortgage-Backed Securities [Line Items]
Mortgage-backed securities, at fair value	$ 6,903	$ 7,931
Amortized Cost	$ 6,949	$ 7,935
Weighted Average Coupon Rate, Percent	3.59%	3.70%
Fixed Rate [Member] | Greater than three years and less than seven years [Member] | Agency RMBS [Member]
Mortgage-Backed Securities [Line Items]
Mortgage-backed securities, at fair value	$ 331,586	$ 419,295
Amortized Cost	$ 339,800	$ 423,248
Weighted Average Coupon Rate, Percent	3.87%	3.93%
Fixed Rate [Member] | Greater than seven years and less than eleven years [Member] | Agency RMBS [Member]
Mortgage-Backed Securities [Line Items]
Mortgage-backed securities, at fair value	$ 1,253,210	$ 1,221,160
Amortized Cost	$ 1,284,720	$ 1,230,479
Weighted Average Coupon Rate, Percent	3.91%	3.92%
Fixed Rate [Member] | Greater than eleven years [Member] | Agency RMBS [Member]
Mortgage-Backed Securities [Line Items]
Mortgage-backed securities, at fair value	$ 11,908	$ 7,382
Amortized Cost	$ 12,016	$ 7,398
Weighted Average Coupon Rate, Percent	4.05%	3.68%
Interest-Only [Member] | Agency RMBS [Member]
Mortgage-Backed Securities [Line Items]
Mortgage-backed securities, at fair value	$ 14,526	$ 12,205
Amortized Cost	$ 14,264	$ 13,197
Weighted Average Coupon Rate, Percent	4.46%	4.36%
Interest-Only [Member] | Less than three years [Member] | Agency RMBS [Member]
Mortgage-Backed Securities [Line Items]
Mortgage-backed securities, at fair value	$ 1,508	$ 3,357
Amortized Cost	$ 1,962	$ 4,253
Weighted Average Coupon Rate, Percent	4.08%	4.15%
Interest-Only [Member] | Greater than three years and less than seven years [Member] | Agency RMBS [Member]
Mortgage-Backed Securities [Line Items]
Mortgage-backed securities, at fair value	$ 13,018	$ 8,848
Amortized Cost	$ 12,302	$ 8,944
Weighted Average Coupon Rate, Percent	4.55%	4.51%
Interest-Only [Member] | Greater than seven years and less than eleven years [Member] | Agency RMBS [Member]
Mortgage-Backed Securities [Line Items]
Mortgage-backed securities, at fair value	$ 0	$ 0
Amortized Cost	$ 0	$ 0
Weighted Average Coupon Rate, Percent	0.00%	0.00%
Interest-Only [Member] | Greater than eleven years [Member] | Agency RMBS [Member]
Mortgage-Backed Securities [Line Items]
Mortgage-backed securities, at fair value	$ 0	$ 0
Amortized Cost	$ 0	$ 0
Weighted Average Coupon Rate, Percent	0.00%	0.00%

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The fair value as of the balance sheet date of firm holdings in mortgages, mortgage backed securities (investment instruments that represent ownership of an undivided interest in a group of mortgages, where principal and interest from the individual mortgages are used to pay investors' principal and interest on the mortgage backed security) and asset-backed securities that are primarily paid from the cash flows of a discrete pool of receivables or other financial assets (such as credit-card receivables), either fixed or revolving, that by their terms convert into cash within a finite time period. Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 320
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=35711157&loc=d3e42546-110969

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Cost of the investment.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section 50
-Paragraph 6
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=63488139&loc=d3e12121-115841

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