Fair Value of Financial Instruments - Quantitative Information about Significant Unobservable Inputs Used in Valuation of Level 3 Assets and Liabilities Measured at Fair Value (Detail)	9 Months Ended
Sep. 30, 2015 USD ($) $ / shares $ / senior_security $ / loan
Asset-backed Securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 1,105,588,000
Asset-backed Securities \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	5.00%
Prepayment rate	6.00%
Credit support	0.00%
Loss severity	20.00%
Default rate	0.00%
Asset-backed Securities \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	9.00%
Prepayment rate	20.00%
Credit support	70.00%
Loss severity	32.00%
Default rate	12.00%
Asset-backed Securities \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	5.00%
Prepayment rate	13.00%
Credit support	12.00%
Loss severity	27.00%
Default rate	6.00%
Commercial Secured Borrowings
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 65,578,000
Commercial Secured Borrowings \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Spread to swap rate	1.94%
Credit support	23.00%
Commercial Secured Borrowings \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Spread to swap rate	1.95%
Credit support	23.00%
Commercial Secured Borrowings \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Spread to swap rate	1.94%
Credit support	23.00%
Residential Loans Priced To Securitization and Whole Loan Market, Uncommitted to Sell
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 2,032,815,000
Residential Loans Priced To Securitization and Whole Loan Market, Uncommitted to Sell \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
IO Multiple	3.8
Prepayment rate	12.00%
Senior credit spread to TBA (usd per senior security) \| $ / senior_security	3.56
Spread to swap rate	3.73%
Credit support	5.00%
Whole loan spread to TBA (usd per loan) \| $ / loan	2.90
Residential Loans Priced To Securitization and Whole Loan Market, Uncommitted to Sell \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
IO Multiple	4.0
Prepayment rate	15.00%
Senior credit spread to TBA (usd per senior security) \| $ / senior_security	3.56
Spread to swap rate	3.73%
Credit support	5.00%
Whole loan spread to TBA (usd per loan) \| $ / loan	4.27
Residential Loans Priced To Securitization and Whole Loan Market, Uncommitted to Sell \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
IO Multiple	3.8
Prepayment rate	14.00%
Senior credit spread to TBA (usd per senior security) \| $ / senior_security	3.56
Spread to swap rate	3.73%
Credit support	5.00%
Whole loan spread to TBA (usd per loan) \| $ / loan	4.08
Residential Jumbo Hybrid Loans Priced To Whole Loan Market Uncommitted To Sell
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 158,149,000
Residential Jumbo Hybrid Loans Priced To Whole Loan Market Uncommitted To Sell \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Spread to swap rate	1.25%
Residential Jumbo Hybrid Loans Priced To Whole Loan Market Uncommitted To Sell \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Spread to swap rate	1.65%
Residential Jumbo Hybrid Loans Priced To Whole Loan Market Uncommitted To Sell \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Spread to swap rate	1.38%
Residential Loans Priced To Whole Loan Market and Committed to Sell
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 437,704,000
Residential Loans Priced To Whole Loan Market and Committed to Sell \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Committed Sales Price \| $ / shares	$ 102.1
Residential Loans Priced To Whole Loan Market and Committed to Sell \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Committed Sales Price \| $ / shares	103
Residential Loans Priced To Whole Loan Market and Committed to Sell \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Committed Sales Price \| $ / shares	$ 102.4
Residential Loans Held For Investment at Fair Value
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 1,170,246,000
Residential Loans at Lower of Cost or Fair Value
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 1,099,000
Residential Loans at Lower of Cost or Fair Value \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity	13.00%
Residential Loans at Lower of Cost or Fair Value \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity	30.00%
Residential Loans at Lower of Cost or Fair Value \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity	21.00%
Commercial Loans at Fair Value
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 150,852,000
Commercial Loans at Fair Value \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Spread to swap rate	1.95%
Credit support	23.00%
Commercial Loans at Fair Value \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Spread to swap rate	1.95%
Credit support	23.00%
Commercial Loans at Fair Value \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Spread to swap rate	1.95%
Credit support	23.00%
Investment Securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 1,085,224,000
Investment Securities \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	4.00%
Prepayment rate	1.00%
Credit support	0.00%
Loss severity	20.00%
Default rate	0.00%
Investment Securities \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	12.00%
Prepayment rate	35.00%
Credit support	49.00%
Loss severity	65.00%
Default rate	35.00%
Investment Securities \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	7.00%
Prepayment rate	13.00%
Credit support	4.00%
Loss severity	34.00%
Default rate	8.00%
Mortgage servicing rights
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 162,726,000
Mortgage servicing rights \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	8.00%
Prepayment rate	5.00%
Per loan annual cost to service	$ 72
Mortgage servicing rights \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	25.00%
Prepayment rate	55.00%
Per loan annual cost to service	$ 82
Mortgage servicing rights \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	10.00%
Prepayment rate	12.00%
Per loan annual cost to service	$ 78
Guarantee asset
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 5,120,000
Guarantee asset \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	10.00%
Prepayment rate	16.00%
Guarantee asset \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	10.00%
Prepayment rate	16.00%
Guarantee asset \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	10.00%
Prepayment rate	16.00%
REO
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 3,120,000
REO \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity	0.00%
REO \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity	89.00%
REO \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity	52.00%
Loan Purchase Commitments
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 9,687,000
Loan Purchase Commitments \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
MSR Multiple	0
Fallout rate	2.00%
Loan Purchase Commitments \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
MSR Multiple	5.0
Fallout rate	98.00%
Loan Purchase Commitments \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
MSR Multiple	3.0
Fallout rate	34.00%

Fair Value Inputs, Committed Sales Price

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- Definition

Fair Value Inputs, Credit Spreads

+ References

No definition available.

+ Details

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- Definition

Percentage of credit support for financial asset.

+ References

No definition available.

+ Details

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- Definition

Fair Value Inputs, Fallout Rate

+ References

No definition available.

+ Details

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- Definition

Fair Value Inputs, Interest Only (IO) Multiple

+ References

No definition available.

+ Details

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- Definition

Fair Value Inputs, Mortgage Servicing Right (MSR) Multiple

+ References

No definition available.

+ Details

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- Definition

Fair Value Inputs, Per Loan Annual Cost To Service

+ References

No definition available.

+ Details

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- Definition

Fair Value Inputs, Subordinate Spread To Swap

+ References

No definition available.

+ Details

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- Definition

Fair Value Inputs, Whole Loan Spread

+ References

No definition available.

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ References

+ Details

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- Definition

Loss, including interest and principal, incurred on a defaulted security, expressed as a percentage of the original principal balance, used as an input to measure fair value.

+ References

+ Details

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- Definition

Rate at which loans or a loan portfolio are expected to prepay principal balances, used as an input to measure fair value.

+ References

+ Details

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Period Type:	duration

- Definition

Percentage of likelihood a loan will not be repaid and instead default, used as an input to measure fair value.

+ References

+ Details

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- Definition

Fair value of financial instrument classified as derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19279-110258

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