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Long-Term Debt - Additional Information (Details) - USD ($) | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | ---
Jun. 30, 2018 | Aug. 31, 2017 | Jan. 31, 2016 | Nov. 30, 2014 | Mar. 31, 2013 | Sep. 30, 2018 | Sep. 30, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Apr. 30, 2018
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Transition period for subsidiary to be a FHLB-member (in years) |  |  |  | 5 years |  |  |  |  |  |  |
Existing debt |  |  |  |  |  |  | $ 0 | $ 0 | $ 0 |  |
Federal home loan bank stock |  |  |  |  |  |  | 43,393,000 | 43,393,000 | 43,393,000 |  |
Accrued interest payable |  |  |  |  |  |  | 3,000,000 | 3,000,000 | 2,000,000 |  |
Notional amount |  |  |  |  |  |  | 6,645,489,000 | 6,645,489,000 | 6,644,081,000 |  |
Accrued interest payable | [1] |  |  |  |  |  | $ 31,076,000 | $ 31,076,000 | 18,435,000 |  |
Trust Preferred Securities And Subordinated Notes |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Weighted average interest rates, by series |  |  |  |  |  |  | 6.90% | 6.90% |  |  |
Accrued interest payable |  |  |  |  |  |  | $ 1,000,000 | $ 1,000,000 | 1,000,000 |  |
Trust Preferred Securities And Subordinated Notes | Interest rate swaps |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Notional amount |  |  |  |  |  |  | 140,000,000 | $ 140,000,000 |  |  |
Trust Preferred Securities And Subordinated Notes | LIBOR |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  |  |  | 2.25% |  |  |
Trust Preferred Securities |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount |  |  |  |  |  |  | 100,000,000 | $ 100,000,000 |  |  |
Subordinated Notes |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt instrument face amount |  |  |  |  |  |  | 40,000,000 | 40,000,000 |  |  |
Senior Notes Due 2024 | Convertible Debt |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Convertible notes |  | $ 200,000,000 |  |  |  |  | 200,000,000 | $ 200,000,000 |  |  |
Debt Instrument interest rate |  | 5.625% |  |  |  |  |  |  |  |  |
Debt instrument, percent of par |  | 99.50% |  |  |  |  |  |  |  |  |
Net proceeds from issuance of convertible debt |  | $ 194,000,000 |  |  |  |  |  |  |  |  |
Interest expense yield |  |  |  |  |  |  |  | 6.20% |  |  |
Convertible senior notes conversion rate |  |  |  |  |  |  |  | 0.0547645 |  |  |
Convertible senior notes conversion per share (in dollars per share) |  | $ 18.26 |  |  |  |  |  |  |  |  |
Accrued interest payable |  |  |  |  |  |  | 3,000,000 | $ 3,000,000 |  |  |
Unamortized debt issuance costs |  |  |  |  |  |  | 5,000,000 | 5,000,000 |  |  |
Unamortized discount |  |  |  |  |  |  | (1,000,000) | (1,000,000) |  |  |
Senior Notes Due 2023 | Convertible Debt |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Convertible notes |  |  | $ 245,000,000 |  |  |  | $ 245,000,000 | $ 245,000,000 |  |  |
Debt Instrument interest rate |  |  | 4.75% |  |  |  |  |  |  |  |
Net proceeds from issuance of convertible debt |  |  | $ 238,000,000 |  |  |  |  |  |  |  |
Interest expense yield |  |  |  |  |  |  |  | 5.30% |  |  |
Convertible senior notes conversion rate |  |  |  |  |  |  |  | 0.0539060 |  |  |
Convertible senior notes conversion per share (in dollars per share) |  |  |  |  |  |  | $ 18.55 | $ 18.55 |  |  |
Accrued interest payable |  |  |  |  |  |  | $ 1,000,000 | $ 1,000,000 |  |  |
Unamortized debt issuance costs |  |  |  |  |  |  | 6,000,000 | 6,000,000 |  |  |
Debt instrument maturity year |  |  | 2023 |  |  |  |  |  |  |  |
Exchangeable Senior Notes Due 2019 | Convertible Debt |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Convertible notes |  |  |  |  | $ 205,000,000 |  | $ 201,000,000 | $ 201,000,000 |  |  |
Debt Instrument interest rate |  |  |  |  | 5.625% |  |  |  |  |  |
Net proceeds from issuance of convertible debt |  |  |  |  | $ 198,000,000 |  |  |  |  |  |
Interest expense yield |  |  |  |  |  |  |  | 6.30% |  |  |
Convertible senior notes conversion rate |  |  |  |  |  |  |  | 0.0462370 |  |  |
Convertible senior notes conversion per share (in dollars per share) |  |  |  |  |  |  | $ 21.63 | $ 21.63 |  |  |
Accrued interest payable |  |  |  |  |  |  | $ 4,000,000 | $ 4,000,000 |  |  |
Unamortized debt issuance costs |  |  |  |  |  |  | $ 1,000,000 | $ 1,000,000 |  |  |
Debt instrument maturity year |  |  |  |  | 2019 |  |  |  |  |  |
Debt instrument redemption date |  |  |  |  |  |  |  | Nov. 15, 2019 |  |  |
Amount of debt repurchased |  |  |  |  |  |  |  |  |  | $ 4,000,000 |
Exchangeable Senior Notes Due 2019 | Convertible Debt | Gain (loss) on investments |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Gain on extinguishment of debt |  |  |  |  |  |  |  |  |  | $ 300,000 |
Convertible Senior Notes Due 2018 | Convertible Debt |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Convertible notes |  |  |  |  |  | $ 288,000,000 |  |  | 288,000,000 |  |
Debt Instrument interest rate |  |  |  |  |  | 4.625% |  |  |  |  |
Net proceeds from issuance of convertible debt |  |  |  |  |  | $ 279,000,000 |  |  |  |  |
Interest expense yield |  |  |  |  |  |  |  | 4.80% |  |  |
Convertible senior notes conversion rate |  |  |  |  |  |  |  | 0.0411320 |  |  |
Convertible senior notes conversion per share (in dollars per share) |  |  |  |  |  |  | $ 24.31 | $ 24.31 |  |  |
Amount of debt repurchased |  |  |  |  |  |  |  |  | 37,000,000 |  | $ 250,000,000
Gain on extinguishment of debt |  |  |  |  |  |  |  |  | (1,000,000) |  |
Unamortized deferred issuance costs |  |  |  |  |  |  |  |  | 2,000,000 |  |
FHLB Chicago |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Federal home loan bank advances, reset period of basis margin (in days) |  |  |  |  |  |  |  | 91 days |  |  |
FHLB Chicago | FHLB Member Subsidiary |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Maximum borrowing limit |  |  |  |  |  |  | $ 2,000,000,000 | $ 2,000,000,000 |  |  |
Additional borrowings from FHLBC |  |  |  |  |  |  | 0 | 0 |  |  |
Existing debt |  |  |  |  |  |  | 2,000,000,000 | 2,000,000,000 |  |  |
Federal home loan bank advances outstanding |  |  |  |  |  |  | $ 2,000,000,000 | $ 2,000,000,000 | $ 2,000,000,000 |  |
Weighted average interest rate |  |  |  |  |  |  | 2.24% | 2.24% | 1.38% |  |
Weighted average maturity (in years) |  |  |  |  |  |  |  | 7 years | 8 years |  |
FHLB Chicago | Redwood | Held-for-sale residential loans | Residential Real Estate |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Loans pledged as collateral under borrowing agreement with FHLBC |  |  |  |  |  |  | $ 2,270,000,000 | $ 2,270,000,000 |  |  |
FHLB Chicago | Redwood | Held-for-sale residential loans | Restricted cash |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Loans pledged as collateral under borrowing agreement with FHLBC |  |  |  |  |  |  | $ 25,000,000 | $ 25,000,000 |  |  |
[1] | Our consolidated balance sheets include assets of consolidated variable interest entities (“VIEs”) that can only be used to settle obligations of these VIEs and liabilities of consolidated VIEs for which creditors do not have recourse to Redwood Trust, Inc. or its affiliates. At September 30, 2018 and December 31, 2017, assets of consolidated VIEs totaled $3,693,140 and $1,259,774, respectively. At September 30, 2018 and December 31, 2017, liabilities of consolidated VIEs totaled $3,417,835 and $1,167,157, respectively. See Note 4 for further discussion.

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- Definition Carrying value as of the balance sheet date of [accrued] interest payable on all forms of debt, including trade payables, that has been incurred and is unpaid. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=82887183&loc=d3e7018-107765 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=82887183&loc=d3e6935-107765 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.20) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
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