Fair Value of Financial Instruments (Details) (USD $)	Sep. 30, 2011	Dec. 31, 2010
Assets:
Agency MBS	$ 7,519,002,000	$ 5,980,623,000
Non-Agency MBS, including MBS transferred to consolidated VIEs	3,889,310,000	2,078,087,000
Linked Transactions	64,494,000	179,915,000
Derivative hedging instruments	81,000
Liabilities:
Derivative hedging instruments	134,712,000	139,142,000
Recurring basis \| Level 2
Assets:
Agency MBS	7,519,002,000
Non-Agency MBS, including MBS transferred to consolidated VIEs	3,889,310,000
Linked Transactions	64,494,000
Derivative hedging instruments	81,000
Total assets carried at fair value	11,472,887,000
Liabilities:
Derivative hedging instruments	134,712,000
Total liabilities carried at fair value	134,712,000
Recurring basis \| Estimated fair value
Assets:
Agency MBS	7,519,002,000
Non-Agency MBS, including MBS transferred to consolidated VIEs	3,889,310,000
Linked Transactions	64,494,000
Derivative hedging instruments	81,000
Total assets carried at fair value	11,472,887,000
Liabilities:
Derivative hedging instruments	134,712,000
Total liabilities carried at fair value	$ 134,712,000

For an unclassified balance sheet, this item Agency MBS represents investments in debt and equity securities which are categorized neither as held-to-maturity nor trading. Such securities are reported at fair value, with unrealized gains and losses excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale Security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain or loss of an Available-for-sale Security that is designated as being hedged in a fair value hedge shall be recognized in earnings during the period of the hedge, as should other than temporary declines in fair value below costs basis.

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- Definition

Represents the fair value of available-for-sale securities not guaranteed by an agency of U.S. Government or any federally chartered corporation, including such securities transferred to a consolidated variable interest entity

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- Definition

The fair value of forward contracts to repurchase mortgage-backed securities.

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- Definition

This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

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Fair value of derivative asset, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (a),(c)

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624163-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 44C

-Subparagraph a

-Clause 1

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 205G

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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Fair value of derivative liability, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

+ References

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This element represents the aggregate of the liabilities reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

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