Repurchase Agreements (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
Sep. 30, 2012 Agreements	Dec. 31, 2011 Agreements
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Debt, Weighted Average Interest Rate	0.63%	0.61%
Number of Agreement Borrowings Outstanding	21	20
Available Repurchase Agreement Counterparties	28
Concentration Risk, Percentage	18.00%
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount	$ 3,670,972	$ 2,093,793
Fair value of Collateral Pledged	4,045,087	2,268,312
Deferred Costs	(764)
Weighted Average Maturity of Agreements	52 days	57 days
Agency RMBS [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Debt, Weighted Average Interest Rate	0.41%	0.38%
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount	2,560,779	1,447,508
Fair value of Collateral Pledged	2,665,860	1,521,107
Agency CMBS and CMBS IO [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Debt, Weighted Average Interest Rate	0.93%	0.59%
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount	634,327	290,362
Fair value of Collateral Pledged	789,792	329,612
Non-Agency RMBS [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Debt, Weighted Average Interest Rate	1.82%	1.85%
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount	11,042	12,195
Fair value of Collateral Pledged	12,761	13,597
Non-Agency CMBS and CMBS IO [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Debt, Weighted Average Interest Rate	1.39%	1.54%
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount	431,039	283,266
Fair value of Collateral Pledged	540,332	336,124
Bonds [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Debt, Weighted Average Interest Rate	1.67%	1.65%
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount	34,549	60,462
Fair value of Collateral Pledged	$ 36,342	$ 67,872

Assets Sold Under Agreements to Repurchase, Number of Agreement Borrowings Available

No definition available.

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- Definition

Number of Agreement Borrowings Outstanding held by the entity.

+ References

No definition available.

+ Details

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- Definition

Represents the percentage of equity at risk under all repurchase agreements with a particular counterparty where equity at risk is defined as the excess of carrying amount (or market value, if higher than the carrying amount) of the securities or other assets pledged as collateral to secure the repurchase agreement borrowings over the amount of the repurchase liability outstanding.

+ References

No definition available.

+ Details

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- Details

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- Definition

Reflects the calculation as of the balance sheet date of the average interest rate weighted by the amount of debt outstanding by type or by instrument at that time.

+ References

No definition available.

+ Details

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- Definition

The carrying amount of deferred costs.

+ References

No definition available.

+ Details

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- Definition

The carrying amount as of the date of the latest financial statement presented of mortgage-related securities classified as available for sale or held for investment which are owned but transferred to another party to serve as collateral to partially or fully secure a debt obligation, repurchase agreement or other current or potential obligation, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 50

-Paragraph 1A

-Subparagraph (b)(1)(i)

-URI http://asc.fasb.org/extlink&oid=7523297&loc=SL6224234-111729

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

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS140-4/FIN46(R)-8

-Paragraph B6

-Subparagraph b

-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 140

-Paragraph 17

-Subparagraph a(2)

-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.

+ Details

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Balance Type:	debit
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- Definition

Weighted average maturity (weighted by amount of the agreement) of repurchase agreements with the counterparty, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 08

-Paragraph m

-Subparagraph 1

-Article 4

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(m)(1)(i)(B)(iii))

-URI http://asc.fasb.org/extlink&oid=6881521&loc=d3e23780-122690

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- Definition

Carrying amount of liabilities associated with financial assets accounted for as secured borrowings recognized in the transferor's statement of financial position at the end of each period presented.

+ References

+ Details

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Balance Type:	credit
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