Fair Value of Financial Instruments - Quantitative Information about Significant Unobservable Inputs Used in Valuation of Level 3 Assets and Liabilities Measured at Fair Value (Details)	12 Months Ended
Dec. 31, 2017 USD ($) $ / loan
ABS Issued Securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 1,164,585,000
ABS Issued Securities \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Prepayment rate (annual CPR)	8.00%
Loss severity	20.00%
Discount rate	3.00%
Default rate	0.00%
ABS Issued Securities \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Prepayment rate (annual CPR)	25.00%
Loss severity	54.00%
Discount rate	15.00%
Default rate	16.00%
ABS Issued Securities \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Prepayment rate (annual CPR)	17.00%
Loss severity	23.00%
Discount rate	4.00%
Default rate	3.00%
Jumbo fixed rate loans
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 3,372,329,000
Jumbo fixed rate loans \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan spread to TBA price (in dollars per loan) \| $ / loan	2.25
Whole loan spread to swap rate	1.75%
Jumbo fixed rate loans \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan spread to TBA price (in dollars per loan) \| $ / loan	3.11
Whole loan spread to swap rate	2.25%
Jumbo fixed rate loans \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan spread to TBA price (in dollars per loan) \| $ / loan	3.09
Whole loan spread to swap rate	2.24%
Jumbo hybrid loans
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 251,847,000
Jumbo hybrid loans \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan spread to swap rate	1.00%
Prepayment rate (annual CPR)	15.00%
Jumbo hybrid loans \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan spread to swap rate	1.85%
Prepayment rate (annual CPR)	15.00%
Jumbo hybrid loans \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan spread to swap rate	1.59%
Prepayment rate (annual CPR)	15.00%
Jumbo loans committed to sell
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 237,262,000
Jumbo loans committed to sell \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan committed sales price (in dollars per loan) \| $ / loan	100.78
Jumbo loans committed to sell \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan committed sales price (in dollars per loan) \| $ / loan	103.01
Jumbo loans committed to sell \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan committed sales price (in dollars per loan) \| $ / loan	101.42
Legacy Sequoia
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 632,817,000
Sequoia Choice
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	620,062,000
Residential loans, at lower of cost or fair value
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 854,000
Residential loans, at lower of cost or fair value \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity	12.00%
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	18.00%
Trading and AFS securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 1,476,510,000
Trading and AFS securities \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Prepayment rate (annual CPR)	0.00%
Loss severity	0.00%
Discount rate	3.00%
Default rate	0.00%
Trading and AFS securities \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Prepayment rate (annual CPR)	50.00%
Loss severity	40.00%
Discount rate	15.00%
Default rate	27.00%
Trading and AFS securities \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Prepayment rate (annual CPR)	10.00%
Loss severity	22.00%
Discount rate	5.00%
Default rate	3.00%
MSRs
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 63,598,000
MSRs \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Prepayment rate (annual CPR)	5.00%
Discount rate	10.00%
Per loan annual cost to service (in dollars per loan)	$ 79
MSRs \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Prepayment rate (annual CPR)	26.00%
Discount rate	130.00%
Per loan annual cost to service (in dollars per loan)	$ 82
MSRs \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Prepayment rate (annual CPR)	9.00%
Discount rate	11.00%
Per loan annual cost to service (in dollars per loan)	$ 82
Guarantee asset
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 2,869,000
Guarantee asset \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Prepayment rate (annual CPR)	13.00%
Discount rate	11.00%
Guarantee asset \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Prepayment rate (annual CPR)	13.00%
Discount rate	11.00%
Guarantee asset \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Prepayment rate (annual CPR)	13.00%
Discount rate	11.00%
REO
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 2,034,000
REO \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity	6.00%
REO \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity	42.00%
REO \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity	21.00%
Loan purchase commitments
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 462,000
Loan purchase commitments \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan spread to TBA price (in dollars per loan) \| $ / loan	2.25
Whole loan spread to swap rate	1.75%
Prepayment rate (annual CPR)	15.00%
MSR multiple	1.7
Pull-through rate	9.00%
Whole loan spread to swap rate - hybrid	1.00%
Loan purchase commitments \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan spread to TBA price (in dollars per loan) \| $ / loan	3.10
Whole loan spread to swap rate	2.25%
Prepayment rate (annual CPR)	15.00%
MSR multiple	5.1
Pull-through rate	100.00%
Whole loan spread to swap rate - hybrid	1.85%
Loan purchase commitments \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan spread to TBA price (in dollars per loan) \| $ / loan	3.06
Whole loan spread to swap rate	2.25%
Prepayment rate (annual CPR)	15.00%
MSR multiple	3.6
Pull-through rate	75.00%
Whole loan spread to swap rate - hybrid	1.51%

Fair Value Inputs, Credit Spreads, Hybrid

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- Definition

Fair Value Inputs, Mortgage Servicing Right (MSR) Multiple

+ References

No definition available.

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- Definition

Fair Value Inputs, Per Loan Annual Cost To Service

+ References

No definition available.

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- Definition

Fair Value Inputs, Pull Through Rate

+ References

No definition available.

+ Details

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- Definition

Fair Value Inputs, Whole Loan Committed Sales Price

+ References

No definition available.

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- Definition

Fair Value Inputs Whole Loan Credit Spreads

+ References

No definition available.

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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

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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

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- Definition

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

+ References

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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 (a)
-URI http://asc.fasb.org/extlink&oid=66048111&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=66048111&loc=d3e19279-110258

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