Repurchase Agreements (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Repurchase Agreements Accounted for as Secured Borrowings	$ 3,185,843		$ 3,013,110
Repurchage agreement, Weighted Average Interest Rate	0.56%		0.55%
Fair Value of Collateral Pledged	3,478,141		3,274,597
Repurchase Agreement Counterparty, Weighted Average Maturity of Agreements	116 days	144 days
Collateralized Mortgage Obligations [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Repurchase Agreements Accounted for as Secured Borrowings	9,122		9,834
Repurchage agreement, Weighted Average Interest Rate	1.53%		1.51%
Fair Value of Collateral Pledged	10,208		11,000
Residential Mortgage Backed Securities [Member] \| Agency MBS [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Repurchase Agreements Accounted for as Secured Borrowings	1,901,144		1,977,338
Repurchage agreement, Weighted Average Interest Rate	0.40%		0.39%
Fair Value of Collateral Pledged	1,975,547		2,064,704
Residential Mortgage Backed Securities [Member] \| Non-Agency MBS [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Repurchase Agreements Accounted for as Secured Borrowings	59,396		17,594
Repurchage agreement, Weighted Average Interest Rate	1.54%		1.57%
Fair Value of Collateral Pledged	72,524		21,787
Commercial Mortgage Backed Securities [Member] \| Agency MBS [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Repurchase Agreements Accounted for as Secured Borrowings	451,290		253,857
Repurchage agreement, Weighted Average Interest Rate	0.36%		0.36%
Fair Value of Collateral Pledged	521,934		291,103
Commercial Mortgage Backed Securities [Member] \| Non-Agency MBS [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Repurchase Agreements Accounted for as Secured Borrowings	143,107		114,895
Repurchage agreement, Weighted Average Interest Rate	1.07%		1.15%
Fair Value of Collateral Pledged	167,759		140,216
CMBS IO [Member] \| Agency MBS [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Repurchase Agreements Accounted for as Secured Borrowings	346,527		372,609
Repurchage agreement, Weighted Average Interest Rate	0.93%		0.92%
Fair Value of Collateral Pledged	404,410		430,638
CMBS IO [Member] \| Non-Agency MBS [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Repurchase Agreements Accounted for as Secured Borrowings	275,257		266,983
Repurchage agreement, Weighted Average Interest Rate	1.05%		1.04%
Fair Value of Collateral Pledged	$ 325,759		$ 315,149

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Interest rate on the amount to be repaid to the counterparty to the repurchase agreement when the carrying amount (or market value, if higher than the carrying amount) of securities or other assets sold under the repurchase agreement exceeds 10 percent of total assets.

+ 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)(A)(ii))

-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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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=26873400&loc=d3e23780-122690

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- Definition

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

+ 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)

-URI http://asc.fasb.org/extlink&oid=34720971&loc=SL6224234-111729

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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

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