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)	3 Months Ended
Mar. 31, 2018 USD ($) $ / loan
ABS Issued
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 1,542,087,000
ABS Issued \| 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 \| 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 \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Prepayment rate (annual CPR)	18.00%
Loss severity	22.00%
Discount rate	4.00%
Default rate	3.00%
Loan Forward Sales Commitments
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 1,269,000
Loan Forward Sales Commitments \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan spread to TBA (in dollars per loan) \| $ / loan	2.80
Loan Forward Sales Commitments \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan spread to TBA (in dollars per loan) \| $ / loan	2.80
Loan Forward Sales Commitments \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan spread to TBA (in dollars per loan) \| $ / loan	2.80
Residential Loans Priced To Securitization and Whole Loan Market, Uncommitted to Sell
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 3,162,491,000
Residential Loans Priced To Securitization and Whole Loan Market, Uncommitted to Sell \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan spread to TBA (in dollars per loan) \| $ / loan	1.78
Whole loan spread to swap rate	1.60%
Residential Loans Priced To Securitization and Whole Loan Market, Uncommitted to Sell \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan spread to TBA (in dollars per loan) \| $ / loan	2.97
Whole loan spread to swap rate	2.10%
Residential Loans Priced To Securitization and Whole Loan Market, Uncommitted to Sell \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan spread to TBA (in dollars per loan) \| $ / loan	2.90
Whole loan spread to swap rate	2.00%
Residential Jumbo Hybrid Loans Priced To Whole Loan Market Uncommitted To Sell
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 258,789,000
Residential Jumbo Hybrid Loans Priced To Whole Loan Market Uncommitted To Sell \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan spread to swap rate	0.90%
Prepayment rate (annual CPR)	15.00%
Residential Jumbo Hybrid Loans Priced To Whole Loan Market Uncommitted To Sell \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan spread to swap rate	1.65%
Prepayment rate (annual CPR)	15.00%
Residential Jumbo Hybrid Loans Priced To Whole Loan Market Uncommitted To Sell \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan spread to swap rate	1.48%
Prepayment rate (annual CPR)	15.00%
Residential Loans Priced To Whole Loan Market and Committed to Sell
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 84,395,000
Residential Loans Priced To Whole Loan Market and Committed to Sell \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan committed sales price (in dollars per loan) \| $ / loan	100.56
Residential Loans Priced To Whole Loan Market and Committed to Sell \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan committed sales price (in dollars per loan) \| $ / loan	101.32
Residential Loans Priced To Whole Loan Market and Committed to Sell \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan committed sales price (in dollars per loan) \| $ / loan	101.12
Legacy Sequoia
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 626,151,000
Sequoia Choice
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	1,013,619,000
Residential loans, at lower of cost or fair value
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 251,000
Residential loans, at lower of cost or fair value \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity	30.00%
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	30.00%
Investment Securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 1,357,720,000
Investment 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%
Investment Securities \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Prepayment rate (annual CPR)	50.00%
Loss severity	40.00%
Discount rate	14.00%
Default rate	27.00%
Investment Securities \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Prepayment rate (annual CPR)	9.00%
Loss severity	22.00%
Discount rate	6.00%
Default rate	3.00%
MSRs
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 66,496,000
MSRs \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Prepayment rate (annual CPR)	6.00%
Discount rate	11.00%
Per loan annual cost to service	$ 79
MSRs \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Prepayment rate (annual CPR)	27.00%
Discount rate	29.00%
Per loan annual cost to service	$ 82
MSRs \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Prepayment rate (annual CPR)	7.00%
Discount rate	11.00%
Per loan annual cost to service	$ 82
Guarantee asset
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 3,055,000
Guarantee asset \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Prepayment rate (annual CPR)	9.00%
Discount rate	11.00%
Guarantee asset \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Prepayment rate (annual CPR)	9.00%
Discount rate	11.00%
Guarantee asset \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Prepayment rate (annual CPR)	9.00%
Discount rate	11.00%
REO
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 2,260,000
REO \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity	12.00%
REO \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity	43.00%
REO \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity	26.00%
Loan purchase commitments
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 1,395,000
Loan purchase commitments \| Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan spread to TBA (in dollars per loan) \| $ / loan	1.78
Whole loan spread to swap rate	2.01%
Prepayment rate (annual CPR)	15.00%
MSR Multiple	1.0
Pull-through rate	9.00%
Whole loan spread to swap rate - hybrid	0.90%
Loan purchase commitments \| Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan spread to TBA (in dollars per loan) \| $ / loan	2.78
Whole loan spread to swap rate	2.01%
Prepayment rate (annual CPR)	15.00%
MSR Multiple	5.2
Pull-through rate	100.00%
Whole loan spread to swap rate - hybrid	1.65%
Loan purchase commitments \| Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Whole loan spread to TBA (in dollars per loan) \| $ / loan	2.77
Whole loan spread to swap rate	2.01%
Prepayment rate (annual CPR)	15.00%
MSR Multiple	3.4
Pull-through rate	68.00%
Whole loan spread to swap rate - hybrid	1.19%

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.

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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.

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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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- 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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