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Valuation Schedule of Fair Value Measurements (Details) - USD ($) $ in Thousands | Sep. 30, 2018 | Dec. 31, 2017
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial derivatives-assets, at fair value | [1] | $ 23,049 | $ 8,792
Financial derivatives–liabilities, at fair value | [1] | (333) | (1,863)
Fair Value, Measurements, Recurring [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 1,575,983 | 1,685,998
Financial derivatives-assets, at fair value |  | 23,049 | 8,792
Total mortgage-backed securities and financial derivatives–assets, at fair value |  | 1,599,032 | 1,694,790
Financial derivatives–liabilities, at fair value |  | (333) | (1,863)
Total U.S. Treasury securities and financial derivatives-liabilities, at fair value |  | (26,700) | (83,152)
Fair Value, Measurements, Recurring [Member] | TBA securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial derivatives-assets, at fair value |  | 1,447 | 402
Financial derivatives–liabilities, at fair value |  | (320) | (735)
Fair Value, Measurements, Recurring [Member] | Interest Rate Swap [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial derivatives-assets, at fair value |  | 18,189 | 8,038
Financial derivatives–liabilities, at fair value |  | (13) | (1,128)
Fair Value, Measurements, Recurring [Member] | Swaption [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial derivatives-assets, at fair value |  |  | 181
Fair Value, Measurements, Recurring [Member] | Futures [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial derivatives-assets, at fair value |  | 3,413 | 171
Fair Value, Measurements, Recurring [Member] | Agency RMBS [Member] | 15-year fixed rate mortgages [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 145,769 | 176,774
Fair Value, Measurements, Recurring [Member] | Agency RMBS [Member] | 20-year fixed rate mortgages [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 7,866 | 9,230
Fair Value, Measurements, Recurring [Member] | Agency RMBS [Member] | 30-year fixed rate mortgages [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 1,297,612 | 1,369,589
Fair Value, Measurements, Recurring [Member] | Agency RMBS [Member] | Adjustable Rate Mortgages |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 19,051 | 29,558
Fair Value, Measurements, Recurring [Member] | Agency RMBS [Member] | Reverse mortgages [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 75,049 | 70,617
Fair Value, Measurements, Recurring [Member] | Agency RMBS [Member] | Interest-Only [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 18,684 | 12,205
Fair Value, Measurements, Recurring [Member] | Non-Agency RMBS [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 11,952 | 18,025
Fair Value, Measurements, Recurring [Member] | US Treasury Securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
U.S. Treasury securities sold short, at fair value |  | (26,367) | (81,289)
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 0 | 0
Financial derivatives-assets, at fair value |  | 3,413 | 171
Total mortgage-backed securities and financial derivatives–assets, at fair value |  | 3,413 | 171
Financial derivatives–liabilities, at fair value |  | 0 | 0
Total U.S. Treasury securities and financial derivatives-liabilities, at fair value |  | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | TBA securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial derivatives-assets, at fair value |  | 0 | 0
Financial derivatives–liabilities, at fair value |  | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Interest Rate Swap [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial derivatives-assets, at fair value |  | 0 | 0
Financial derivatives–liabilities, at fair value |  | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Swaption [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial derivatives-assets, at fair value |  |  | 0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Futures [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial derivatives-assets, at fair value |  | 3,413 | 171
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Agency RMBS [Member] | 15-year fixed rate mortgages [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Agency RMBS [Member] | 20-year fixed rate mortgages [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Agency RMBS [Member] | 30-year fixed rate mortgages [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Agency RMBS [Member] | Adjustable Rate Mortgages |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Agency RMBS [Member] | Reverse mortgages [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Agency RMBS [Member] | Interest-Only [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Non-Agency RMBS [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | US Treasury Securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
U.S. Treasury securities sold short, at fair value |  | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 1,564,242 | 1,674,912
Financial derivatives-assets, at fair value |  | 19,636 | 8,621
Total mortgage-backed securities and financial derivatives–assets, at fair value |  | 1,583,878 | 1,683,533
Financial derivatives–liabilities, at fair value |  | (333) | (1,863)
Total U.S. Treasury securities and financial derivatives-liabilities, at fair value |  | (26,700) | (83,152)
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | TBA securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial derivatives-assets, at fair value |  | 1,447 | 402
Financial derivatives–liabilities, at fair value |  | (320) | (735)
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Interest Rate Swap [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial derivatives-assets, at fair value |  | 18,189 | 8,038
Financial derivatives–liabilities, at fair value |  | (13) | (1,128)
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Swaption [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial derivatives-assets, at fair value |  |  | 181
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Futures [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial derivatives-assets, at fair value |  | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Agency RMBS [Member] | 15-year fixed rate mortgages [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 145,769 | 176,774
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Agency RMBS [Member] | 20-year fixed rate mortgages [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 7,866 | 9,230
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Agency RMBS [Member] | 30-year fixed rate mortgages [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 1,297,612 | 1,369,589
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Agency RMBS [Member] | Adjustable Rate Mortgages |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 19,051 | 29,558
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Agency RMBS [Member] | Reverse mortgages [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 75,049 | 70,617
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Agency RMBS [Member] | Interest-Only [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 14,576 | 9,951
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Non-Agency RMBS [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 4,319 | 9,193
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | US Treasury Securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
U.S. Treasury securities sold short, at fair value |  | (26,367) | (81,289)
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 11,741 | 11,086
Financial derivatives-assets, at fair value |  | 0 | 0
Total mortgage-backed securities and financial derivatives–assets, at fair value |  | 11,741 | 11,086
Financial derivatives–liabilities, at fair value |  | 0 | 0
Total U.S. Treasury securities and financial derivatives-liabilities, at fair value |  | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | TBA securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial derivatives-assets, at fair value |  | 0 | 0
Financial derivatives–liabilities, at fair value |  | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Interest Rate Swap [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial derivatives-assets, at fair value |  | 0 | 0
Financial derivatives–liabilities, at fair value |  | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Swaption [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial derivatives-assets, at fair value |  |  | 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Futures [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Financial derivatives-assets, at fair value |  | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Agency RMBS [Member] | 15-year fixed rate mortgages [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Agency RMBS [Member] | 20-year fixed rate mortgages [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Agency RMBS [Member] | 30-year fixed rate mortgages [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Agency RMBS [Member] | Adjustable Rate Mortgages |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Agency RMBS [Member] | Reverse mortgages [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Agency RMBS [Member] | Interest-Only [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 4,108 | 2,254
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Non-Agency RMBS [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | 7,633 | 8,832
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | US Treasury Securities [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
U.S. Treasury securities sold short, at fair value |  | $ 0 | $ 0
[1] | In the Company's Consolidated Balance Sheet, all balances associated with the repurchase agreements and financial derivatives are presented on a gross basis.

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- Definition Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312 + Details
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