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Schedule of Mortgage-Backed Securities by Weighted Average Life (Details) - USD ($) $ in Thousands		Sep. 30, 2018	Dec. 31, 2017
Mortgage-Backed Securities [Line Items]
Mortgage-backed securities, at fair value		$ 1,575,983	$ 1,685,998
Non-Agency RMBS [Member]
Mortgage-Backed Securities [Line Items]
Mortgage-backed securities, at fair value		11,952	18,025
Amortized Cost		$ 9,908	$ 15,278
Weighted Average Coupon Rate, Percent		4.38%	3.58%
Less than three years [Member] | Non-Agency RMBS [Member]
Mortgage-Backed Securities [Line Items]
Mortgage-backed securities, at fair value	[1]	$ 5,033	$ 0
Amortized Cost	[1]	$ 4,259	$ 0
Weighted Average Coupon Rate, Percent	[1]	5.28%	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	[1]	$ 2,611	$ 9,625
Amortized Cost	[1]	$ 2,465	$ 9,062
Weighted Average Coupon Rate, Percent	[1]	5.84%	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	[1]	$ 4,308	$ 5,892
Amortized Cost	[1]	$ 3,184	$ 3,697
Weighted Average Coupon Rate, Percent	[1]	2.69%	2.14%
Greater than eleven years [Member] | Non-Agency RMBS [Member]
Mortgage-Backed Securities [Line Items]
Mortgage-backed securities, at fair value	[1]	$ 0	$ 2,508
Amortized Cost	[1]	$ 0	$ 2,519
Weighted Average Coupon Rate, Percent	[1]	0.00%	2.18%
Fixed Rate [Member] | Agency RMBS [Member]
Mortgage-Backed Securities [Line Items]
Mortgage-backed securities, at fair value		$ 1,545,347	$ 1,655,768
Amortized Cost		$ 1,592,424	$ 1,669,060
Weighted Average Coupon Rate, Percent		4.07%	3.92%
Fixed Rate [Member] | Less than three years [Member] | Agency RMBS [Member]
Mortgage-Backed Securities [Line Items]
Mortgage-backed securities, at fair value	[1]	$ 4,376	$ 7,931
Amortized Cost	[1]	$ 4,451	$ 7,935
Weighted Average Coupon Rate, Percent	[1]	4.12%	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	[1]	$ 312,760	$ 419,295
Amortized Cost	[1]	$ 323,265	$ 423,248
Weighted Average Coupon Rate, Percent	[1]	4.00%	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]	$ 1,208,634	$ 1,221,160
Amortized Cost	[1]	$ 1,244,869	$ 1,230,479
Weighted Average Coupon Rate, Percent	[1]	4.08%	3.92%
Fixed Rate [Member] | Greater than eleven years [Member] | Agency RMBS [Member]
Mortgage-Backed Securities [Line Items]
Mortgage-backed securities, at fair value	[1]	$ 19,577	$ 7,382
Amortized Cost	[1]	$ 19,839	$ 7,398
Weighted Average Coupon Rate, Percent	[1]	3.99%	3.68%
Interest-Only [Member] | Agency RMBS [Member]
Mortgage-Backed Securities [Line Items]
Mortgage-backed securities, at fair value		$ 18,684	$ 12,205
Amortized Cost		$ 17,601	$ 13,197
Weighted Average Coupon Rate, Percent		4.44%	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]	$ 1,132	$ 3,357
Amortized Cost	[1]	$ 1,517	$ 4,253
Weighted Average Coupon Rate, Percent	[1]	4.51%	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	[1]	$ 17,552	$ 8,848
Amortized Cost	[1]	$ 16,084	$ 8,944
Weighted Average Coupon Rate, Percent	[1]	4.43%	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	[1]	$ 0	$ 0
Amortized Cost	[1]	$ 0	$ 0
Weighted Average Coupon Rate, Percent	[1]	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	[1]	$ 0	$ 0
Amortized Cost	[1]	$ 0	$ 0
Weighted Average Coupon Rate, Percent	[1]	0.00%	0.00%
[1] Average lives of RMBS are generally shorter than stated contractual maturities.

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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.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Cost of the investment.

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