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Schedule of Mortgage-Backed Securities (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2018 | Dec. 31, 2017
Mortgage-Backed Securities [Line Items] |  |  |
Mortgage-backed securities, at fair value |  | $ 1,630,575 | $ 1,685,998
Residential Mortgage Backed Securities [Member] |  |  |
Mortgage-Backed Securities [Line Items] |  |  |
Current Principal |  | 1,573,073 | 1,597,984
Unamortized Premium (Discount) |  | 80,915 | 86,354
Amortized Cost |  | 1,668,252 | 1,697,535
Gross Unrealized Gain on Securities |  | 3,744 | 5,474
Gross Unrealized Losses on Securities |  | (41,421) | (17,011)
Mortgage-backed securities, at fair value |  | $ 1,630,575 | $ 1,685,998
Weighted Average Coupon |  | 3.94% | 3.94%
Weighted Average Yield |  | 3.03% | 3.03%
Weighted Average Life (Years) | [1] | 7 years 223 days | 7 years 142 days
Non-Agency RMBS [Member] |  |  |
Mortgage-Backed Securities [Line Items] |  |  |
Current Principal |  | $ 15,258 | $ 21,995
Unamortized Premium (Discount) |  | (4,755) | (6,717)
Amortized Cost |  | 10,503 | 15,278
Gross Unrealized Gain on Securities |  | 2,001 | 2,846
Gross Unrealized Losses on Securities |  | (62) | (99)
Mortgage-backed securities, at fair value |  | $ 12,442 | $ 18,025
Weighted Average Coupon |  | 3.94% | 3.58%
Weighted Average Yield |  | 6.82% | 8.39%
Weighted Average Life (Years) | [1] | 7 years 157 days | 7 years 343 days
15-year fixed rate mortgages [Member] | Agency RMBS [Member] |  |  |
Mortgage-Backed Securities [Line Items] |  |  |
Current Principal |  | $ 151,969 | $ 170,998
Unamortized Premium (Discount) |  | 6,721 | 7,553
Amortized Cost |  | 158,690 | 178,551
Gross Unrealized Gain on Securities |  | 0 | 28
Gross Unrealized Losses on Securities |  | (3,840) | (1,805)
Mortgage-backed securities, at fair value |  | $ 154,850 | $ 176,774
Weighted Average Coupon |  | 3.41% | 3.38%
Weighted Average Yield |  | 2.31% | 2.31%
Weighted Average Life (Years) | [1] | 4 years 230 days | 4 years 274 days
20-year fixed rate mortgages [Member] | Agency RMBS [Member] |  |  |
Mortgage-Backed Securities [Line Items] |  |  |
Current Principal |  | $ 8,432 | $ 8,712
Unamortized Premium (Discount) |  | 646 | 682
Amortized Cost |  | 9,078 | 9,394
Gross Unrealized Gain on Securities |  | 0 | 0
Gross Unrealized Losses on Securities |  | (305) | (164)
Mortgage-backed securities, at fair value |  | $ 8,773 | $ 9,230
Weighted Average Coupon |  | 4.00% | 4.00%
Weighted Average Yield |  | 2.53% | 2.55%
Weighted Average Life (Years) | [1] | 6 years 15 days | 6 years 7 days
30-year fixed rate mortgages [Member] | Agency RMBS [Member] |  |  |
Mortgage-Backed Securities [Line Items] |  |  |
Current Principal |  | $ 1,304,988 | $ 1,303,584
Unamortized Premium (Discount) |  | 70,183 | 76,681
Amortized Cost |  | 1,375,171 | 1,380,265
Gross Unrealized Gain on Securities |  | 416 | 1,929
Gross Unrealized Losses on Securities |  | (34,367) | (12,605)
Mortgage-backed securities, at fair value |  | $ 1,341,220 | $ 1,369,589
Weighted Average Coupon |  | 3.93% | 3.96%
Weighted Average Yield |  | 3.08% | 3.06%
Weighted Average Life (Years) | [1] | 8 years 142 days | 8 years 66 days
Adjustable Rate Mortgages | Agency RMBS [Member] |  |  |
Mortgage-Backed Securities [Line Items] |  |  |
Current Principal |  | $ 22,613 | $ 28,087
Unamortized Premium (Discount) |  | 1,397 | 1,862
Amortized Cost |  | 24,010 | 29,949
Gross Unrealized Gain on Securities |  | 10 | 30
Gross Unrealized Losses on Securities |  | (638) | (421)
Mortgage-backed securities, at fair value |  | $ 23,382 | $ 29,558
Weighted Average Coupon |  | 3.80% | 3.87%
Weighted Average Yield |  | 2.57% | 2.58%
Weighted Average Life (Years) | [1] | 4 years 117 days | 4 years 256 days
Reverse mortgages [Member] | Agency RMBS [Member] |  |  |
Mortgage-Backed Securities [Line Items] |  |  |
Current Principal |  | $ 69,813 | $ 64,608
Unamortized Premium (Discount) |  | 6,723 | 6,293
Amortized Cost |  | 76,536 | 70,901
Gross Unrealized Gain on Securities |  | 166 | 259
Gross Unrealized Losses on Securities |  | (1,320) | (543)
Mortgage-backed securities, at fair value |  | $ 75,382 | $ 70,617
Weighted Average Coupon |  | 4.52% | 4.53%
Weighted Average Yield |  | 2.83% | 2.79%
Weighted Average Life (Years) | [1] | 6 years 18 days | 6 years 33 days
Interest-Only [Member] | Agency RMBS [Member] |  |  |
Mortgage-Backed Securities [Line Items] |  |  |
Amortized Cost |  | $ 14,264 | $ 13,197
Gross Unrealized Gain on Securities |  | 1,151 | 382
Gross Unrealized Losses on Securities |  | (889) | (1,374)
Mortgage-backed securities, at fair value |  | $ 14,526 | $ 12,205
Weighted Average Coupon |  | 4.46% | 4.36%
Weighted Average Yield |  | 5.87% | 5.64%
Weighted Average Life (Years) | [1] | 4 years 62 days | 3 years 102 days
Agency Securities [Member] | Agency RMBS [Member] |  |  |
Mortgage-Backed Securities [Line Items] |  |  |
Current Principal |  | $ 1,557,815 | $ 1,575,989
Unamortized Premium (Discount) |  | 85,670 | 93,071
Amortized Cost |  | 1,657,749 | 1,682,257
Gross Unrealized Gain on Securities |  | 1,743 | 2,628
Gross Unrealized Losses on Securities |  | (41,359) | (16,912)
Mortgage-backed securities, at fair value |  | $ 1,618,133 | $ 1,667,973
Weighted Average Coupon |  | 3.94% | 3.95%
Weighted Average Yield |  | 3.01% | 2.98%
Weighted Average Life (Years) | [1] | 7 years 223 days | 7 years 139 days
[1] | Average lives of RMBS are generally shorter than stated contractual maturities. Average lives are affected by the contractual maturities of the underlying mortgages, scheduled periodic payments of principal, and unscheduled prepayments of principal.

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