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Mortgage Backed Securities Mortgage backed securities designated as AFS (Details) (USD $) In Thousands, unless otherwise specified | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2014 | Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Available-for-sale MBS, Par Balance | $ 2,781,833 |  | $ 3,254,946 |
Available-for-sale MBS, Unamortized Premium (Discount) | 811,251 |  | 758,950 |
Available-for-sale MBS, Amortized Cost | 3,593,084 |  | 4,013,896 |
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax | 54,491 |  | 45,114 |
Available-for-sale MBS, Gross Unrealized Loss | (32,182) |  | (69,566) |
Available-for-sale MBS, Fair Value | 3,615,393 |  | 3,989,444 |
Agency MBS [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Available-for-sale MBS, Par Balance | 2,505,715 |  | 2,865,398 |
Available-for-sale MBS, Unamortized Premium (Discount) | 540,739 |  | 627,047 |
Available-for-sale MBS, Amortized Cost | 3,046,454 |  | 3,492,445 |
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax | 32,340 |  | 26,792 |
Available-for-sale MBS, Gross Unrealized Loss | (31,442) |  | (63,976) |
Available-for-sale MBS, Fair Value | 3,047,352 |  | 3,455,261 |
Agency MBS [Member] | Residential Mortgage Backed Securities [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Available-for-sale MBS, Par Balance | 2,200,149 |  | 2,591,568 |
Available-for-sale MBS, Unamortized Premium (Discount) | 120,667 |  | 154,220 |
Available-for-sale MBS, Amortized Cost | 2,320,816 |  | 2,745,788 |
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax | 7,593 |  | 6,104 |
Available-for-sale MBS, Gross Unrealized Loss | (31,105) |  | (59,742) |
Available-for-sale MBS, Fair Value | 2,297,304 |  | 2,692,150 |
Available-for-sale MBS, Weighted Average Coupon | 3.14% |  | 3.22% |
Agency MBS [Member] | Commercial Mortgage Backed Securities [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Available-for-sale MBS, Par Balance | 305,566 |  | 273,830 |
Available-for-sale MBS, Unamortized Premium (Discount) | 19,186 |  | 19,061 |
Available-for-sale MBS, Amortized Cost | 324,752 |  | 292,891 | [1]
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax | 13,803 |  | 10,793 |
Available-for-sale MBS, Gross Unrealized Loss | (224) |  | (900) |
Available-for-sale MBS, Fair Value | 338,331 |  | 302,784 | [1]
Available-for-sale MBS, Weighted Average Coupon | 5.22% |  | 5.07% |
Agency MBS [Member] | CMBS IO [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Available-for-sale MBS, Par Balance | 0 | [2] | 0 | [3]
Available-for-sale MBS, Unamortized Premium (Discount) | 400,886 |  | 453,766 |
Available-for-sale MBS, Amortized Cost | 400,886 |  | 453,766 |
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax | 10,944 |  | 9,895 |
Available-for-sale MBS, Gross Unrealized Loss | (113) |  | (3,334) |
Available-for-sale MBS, Fair Value | 411,717 |  | 460,327 |
Available-for-sale MBS, Weighted Average Coupon | 0.83% |  | 0.83% |
Notional balance for interest only securities | 9,461,823 |  | 10,160,502 |
Non-Agency MBS [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Available-for-sale MBS, Par Balance | 276,118 |  | 389,548 |
Available-for-sale MBS, Unamortized Premium (Discount) | 270,512 |  | 131,903 |
Available-for-sale MBS, Amortized Cost | 546,630 |  | 521,451 |
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax | 22,151 |  | 18,322 |
Available-for-sale MBS, Gross Unrealized Loss | (740) |  | (5,590) |
Available-for-sale MBS, Fair Value | 568,041 |  | 534,183 |
Non-Agency MBS [Member] | Residential Mortgage Backed Securities [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Available-for-sale MBS, Par Balance | 9,522 |  | 13,845 |
Available-for-sale MBS, Unamortized Premium (Discount) | (4) |  | (338) |
Available-for-sale MBS, Amortized Cost | 9,518 |  | 13,507 |
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax | 118 |  | 338 |
Available-for-sale MBS, Gross Unrealized Loss | (81) |  | (80) |
Available-for-sale MBS, Fair Value | 9,555 |  | 13,765 |
Available-for-sale MBS, Weighted Average Coupon | 4.20% |  | 4.61% |
Non-Agency MBS [Member] | Commercial Mortgage Backed Securities [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Available-for-sale MBS, Par Balance | 266,596 |  | 375,703 |
Available-for-sale MBS, Unamortized Premium (Discount) | (12,374) |  | (18,277) |
Available-for-sale MBS, Amortized Cost | 254,222 |  | 357,426 |
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax | 16,397 |  | 15,366 |
Available-for-sale MBS, Gross Unrealized Loss | (346) |  | (3,511) |
Available-for-sale MBS, Fair Value | 270,273 |  | 369,281 |
Available-for-sale MBS, Weighted Average Coupon | 4.89% |  | 5.10% |
Non-Agency MBS [Member] | CMBS IO [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Available-for-sale MBS, Par Balance | 0 | [2] | 0 | [3]
Available-for-sale MBS, Unamortized Premium (Discount) | 282,890 |  | 150,518 |
Available-for-sale MBS, Amortized Cost | 282,890 |  | 150,518 |
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax | 5,636 |  | 2,618 |
Available-for-sale MBS, Gross Unrealized Loss | (313) |  | (1,999) |
Available-for-sale MBS, Fair Value | 288,213 |  | 151,137 |
Available-for-sale MBS, Weighted Average Coupon | 0.69% |  | 0.66% |
Notional balance for interest only securities | 7,246,832 |  | 4,274,957 |
Agency MBS [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Available-for-sale MBS, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value | 155,501 |  | 1,912,937 |
Available-for-sale MBS, Continuous Unrealized Loss Position, Less than 12 Months, Gross Unrealized Losses | (1,142) |  | (43,543) |
Available-for-sale MBS, Number of Securities in Continuous Unrealized Loss Position for Less than One Year | 25 |  | 150 |
Available-for-sale MBS, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 1,701,638 |  | 670,402 |
Available-for-sale MBS, Continuous Unrealized Loss Position, 12 Months or Longer, Gross Unrealized Losses | (30,299) |  | (20,433) |
Available-for-sale MBS, Number of Securities in Continuous Unrealized Loss Position for Greater than or Equal to One Year | 129 |  | 67 |
Non-Agency MBS [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Available-for-sale MBS, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value | 74,239 |  | 162,558 |
Available-for-sale MBS, Continuous Unrealized Loss Position, Less than 12 Months, Gross Unrealized Losses | (427) |  | (5,435) |
Available-for-sale MBS, Number of Securities in Continuous Unrealized Loss Position for Less than One Year | 17 |  | 39 |
Available-for-sale MBS, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 31,348 |  | 6,310 |
Available-for-sale MBS, Continuous Unrealized Loss Position, 12 Months or Longer, Gross Unrealized Losses | $ (313) |  | $ (155) |
Available-for-sale MBS, Number of Securities in Continuous Unrealized Loss Position for Greater than or Equal to One Year | 8 |  | 6 |
[1] | (1) As of December 31, 2013, the Company had Agency CMBS with an amortized cost of $26,920 and fair value of $28,717 which were designated as trading securities and are not included in this table. The Company changed the designation of these Agency CMBS to AFS during the three months ended June 30, 2014. Changes in the fair value of these MBS while they were designated as trading were recognized in net income within "fair value adjustments, net". Changes in the fair value of these MBS, which are now designated as AFS, are recognized in "other comprehensive income". As of September 30, 2014, the Company does not have any MBS designated as trading.
[2] | (1)The notional balance for Agency CMBS IO and non-Agency CMBS IO was $9,461,823 and $7,246,832, respectively, as of September 30, 2014. December 31, 2013 Par Net Premium (Discount) Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value WACAgency: RMBS$2,591,568 $154,220 $2,745,788 $6,104 $(59,742) $2,692,150 3.22%CMBS (1)273,830 19,061 292,891 10,793 (900) 302,784 5.07%CMBS IO (2)— 453,766 453,766 9,895 (3,334) 460,327 0.83%Total Agency AFS:2,865,398 627,047 3,492,445 26,792 (63,976) 3,455,261 Non-Agency: RMBS13,845 (338) 13,507 338 (80) 13,765 4.61%CMBS375,703 (18,277) 357,426 15,366 (3,511) 369,281 5.10%CMBS IO (2)— 150,518 150,518 2,618 (1,999) 151,137 0.66%Total non-Agency AFS:389,548 131,903 521,451 18,322 (5,590) 534,183 Total AFS securities$3,254,946 $758,950 $4,013,896 $45,114 $(69,566) $3,989,444
[3] | (2) The notional balance for the Agency CMBS IO and non-Agency CMBS IO was $10,160,502 and $4,274,957, respectively, as of December 31, 2013.

X
- Definition The remaining amount of investment premium (discount), net, originally recognized at the purchase date of the instruments that has yet to be amortized (accreted) into earnings. + References No definition available. + Details
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- Definition This item represents the current weighted-average gross interest rate earned on this type of MBS in the investment portfolio as of the period indicated. The gross interest rate of each MBS within the portfolio is weighted based on its current outstanding notional or par balance. The current outstanding notional or par balance for each MBS consists of the total of all principal balances remaining on the mortgage loans underlying each MBS. + References No definition available. + Details
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- Definition Notional balance for interest only securities owned by the Company. Interest only securities represent the right to receive excess interest payments, and not principal cash flows, based on the underlying unpaid principal balance (ie, notional) of the underlying pool of mortgage loans. + References No definition available. + Details
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