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Derivative Instruments and Hedging Activities Schedule of TBA Contracts (Details) (USD $)
In Thousands, unless otherwise specified |
Sep. 30, 2014
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Jun. 30, 2014
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Dec. 31, 2013
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Sep. 30, 2013
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Jun. 30, 2013
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Dec. 31, 2012
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|---|---|---|---|---|---|---|
| Derivative [Line Items] | ||||||
| Derivative, Notional Amount | $ 57,015,981 | $ 43,379,217 | $ 37,366,610 | $ 36,472,401 | $ 44,262,605 | $ 22,377,656 |
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Derivative Financial Instruments, Assets [Member]
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| Derivative [Line Items] | ||||||
| Derivative, Notional Amount | 60,460,981 | 30,383,908 | ||||
| Derivative, Fair Value, Net | 353,893 | 549,859 | ||||
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Derivative Financial Instruments, Liabilities [Member]
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||||||
| Derivative [Line Items] | ||||||
| Derivative, Notional Amount | 2,315,000 | 10,876,702 | ||||
| Derivative, Fair Value, Net | (4,221) | (22,081) | ||||
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Forward Contracts [Member]
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| Derivative [Line Items] | ||||||
| Derivative, Notional Amount | (690,000) | (372,000) | 603,000 | 857,000 | (2,721,000) | 953,000 |
| Derivative, Cost | (787,054) | 790,392 | ||||
| Derivative, Market Value | (785,349) | 823,693 | ||||
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Forward Contracts [Member] | Derivative Financial Instruments, Assets [Member]
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| Derivative [Line Items] | ||||||
| Derivative, Notional Amount | 2,880,000 | 4,097,000 | ||||
| Derivative, Fair Value, Net | 4,101 | 33,425 | ||||
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Forward Contracts [Member] | Derivative Financial Instruments, Liabilities [Member]
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| Derivative [Line Items] | ||||||
| Derivative, Notional Amount | 2,190,000 | 400,000 | ||||
| Derivative, Fair Value, Net | (2,396) | (125) | ||||
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Forward Contracts [Member] | Long [Member]
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| Derivative [Line Items] | ||||||
| Derivative, Notional Amount | 2,190,000 | 2,550,000 | ||||
| Derivative, Cost | 2,149,844 | 2,749,648 | ||||
| Derivative, Market Value | 2,152,274 | 2,767,295 | ||||
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Forward Contracts [Member] | Long [Member] | Derivative Financial Instruments, Assets [Member]
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| Derivative [Line Items] | ||||||
| Derivative, Fair Value, Net | 2,430 | 17,771 | ||||
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Forward Contracts [Member] | Long [Member] | Derivative Financial Instruments, Liabilities [Member]
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| Derivative [Line Items] | ||||||
| Derivative, Fair Value, Net | 0 | (125) | ||||
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Forward Contracts [Member] | Short [Member]
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| Derivative [Line Items] | ||||||
| Derivative, Notional Amount | (2,880,000) | (1,947,000) | ||||
| Derivative, Cost | (2,936,898) | (1,959,256) | ||||
| Derivative, Market Value | (2,937,623) | (1,943,602) | ||||
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Forward Contracts [Member] | Short [Member] | Derivative Financial Instruments, Assets [Member]
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||||||
| Derivative [Line Items] | ||||||
| Derivative, Fair Value, Net | 1,671 | 15,654 | ||||
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Forward Contracts [Member] | Short [Member] | Derivative Financial Instruments, Liabilities [Member]
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| Derivative [Line Items] | ||||||
| Derivative, Fair Value, Net | (2,396) | 0 | ||||
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Agency To-be-Announced Securities, Non-Risk Management [Member] | Long [Member]
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| Derivative [Line Items] | ||||||
| Derivative, Notional Amount | 2,150,000 | |||||
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Interest Rate Risk Associated with the Investment Portfolio [Member] | Forward Contracts [Member] | Long [Member]
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| Derivative [Line Items] | ||||||
| Derivative, Notional Amount | 2,190,000 | 400,000 | ||||
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Interest Rate Risk Associated with the Investment Portfolio [Member] | Forward Contracts [Member] | Short [Member]
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| Derivative [Line Items] | ||||||
| Derivative, Notional Amount | $ 2,880,000 | $ 1,947,000 |