Financial Instruments (Details 2) (USD $)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011
Level 2 \| Agency mortgage-backed securities
Financial Instrument Characteristics
Weighted average loan size	$ 200,000	$ 200,000
Interest rate (as a percent)	0.049	0.062
Weighted average FICO score	728	700
Weighted average coupon rate (as a percent)	4.30%	5.49%
Weighted average annualized constant prepayment rate (as a percent)	17.40%	19.00%
Level 2 \| Federal agency obligations
Financial Instrument Characteristics
Weighted average coupon rate (as a percent)	3.50%	2.30%
Weighted Average Maturity	2019	2022
Level 2 \| Loans
Financial Instrument Characteristics
Weighted average loan size	200,000	300,000
Weighted average coupon rate (as a percent)	3.60%	4.10%
Unpaid principal	75,200,000	221,600,000
Unrealized gain (loss) arising from fair value changes	(300,000)	600,000
Loans 90 days or more past due	0	0
Loans in non-accrual status	0	0
Level 2 \| Corporate debt securities
Financial Instrument Characteristics
Weighted Average Maturity	2024	2017
Weighted Average Credit Rating	BBB	BBB
Weighted Average Issuance Year	2009	2007
Level 2 \| Commercial mortgage-backed securities
Financial Instrument Characteristics
Net holdings	4,900,000
Weighted Average Credit Rating	AA+
Weighted Average Vintage	2007
Level 2 \| Residential mortgage-backed securities
Financial Instrument Characteristics
Net holdings	23,100,000
Weighted Average Credit Rating	CCC
Weighted Average Issuance Year	2005
Level 2 \| Other debt obligations
Financial Instrument Characteristics
Net holdings	2,100,000
Weighted Average Credit Rating	AAA
Weighted Average Vintage	2012
Level 3 \| Agency mortgage-backed securities
Financial Instrument Characteristics
Weighted average loan size		$ 100,000
Interest rate (as a percent)		0.068
Weighted average coupon rate (as a percent)		5.50%
Weighted Average Vintage		2007
Level 3 \| Commercial mortgage-backed securities
Financial Instrument Characteristics
Weighted Average Credit Rating		BBB
Weighted Average Vintage		2006
Level 3 \| Residential mortgage-backed securities
Financial Instrument Characteristics
Weighted Average Credit Rating		CCC
Weighted average default rate (as a percent)		5.90%
Weighted average severity (as a percent)		58.60%

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Represents interest rates for investment owned at fair value excluding principal investments.

+ References

No definition available.

+ Details

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- Definition

Represents weighted average prepayment rate of the underlying financial instruments.

+ References

No definition available.

+ Details

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- Definition

Represents weighted average coupon rate of underlying financial instruments.

+ References

No definition available.

+ Details

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- Definition

Represents the weighted average credit rating of the underlying financial instruments.

+ References

No definition available.

+ Details

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- Definition

Represents the weighted average default rate of the underlying financial instruments.

+ References

No definition available.

+ Details

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- Definition

Represents weighted average FICO score of the underlying financial instruments.

+ References

No definition available.

+ Details

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- Definition

Represents the weighted average maturity of the underlying financial instruments.

+ References

No definition available.

+ Details

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- Definition

Represents the weighted average loan size of the securities.

+ References

No definition available.

+ Details

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- Definition

Represents the weighted average maturity of the underlying financial instruments.

+ References

No definition available.

+ Details

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- Definition

Represents the weighted average severity rate of the underlying financial instruments.

+ References

No definition available.

+ Details

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- Definition

Represents the weighted average vintage of the underlying financial instruments.

+ References

No definition available.

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- Definition

For each line item in the statement of financial position, the amounts of gains and losses from fair value changes included in earnings.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 30

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14172-108612

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- Definition

Financing receivables that are equal to or greater than 90 days past due.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7A

-URI http://asc.fasb.org/extlink&oid=7512638&loc=SL6953401-111524

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- Definition

Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5111-111524

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- Definition

The net of non investment assets and liabilities. This amount represents the difference between the aggregate value of the investments, including long and short positions, and net assets.

+ References

No definition available.

+ Details

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- Definition

This is the result of the principal amount outstanding of total loans managed or securitized less securitized loans and loans that are in the process of being securitized.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 20

-Section 50

-Paragraph 4

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=13989330&loc=d3e107314-111719

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-Publisher FASB

-Name FASB Staff Position (FSP)

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

-Paragraph B11

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-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 i

-Subclause a

-Clause 4

-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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