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Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Significant Accounting Policies [Line Items] |  |  |
Incentive Plan, mandatory holding period before awards vest | 3 years |  |
Employee Stock Purchase Plan, percentage of common stock fair value that employees can purchase | 85.00%rwt_EmployeeStockPurchasePlanMinimumPercentageOfCommonStockFairValueDefinedToPurchaseSharesByEligibleParticipants |  |
Employees maximum 401(k) contribution | 100.00%us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent |  |
Employer matching contributions | $ 0.6 us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount | $ 0.2 us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount | $ 0.3 us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount
Minimum percentage of taxable income distribution to shareholders to be taxed as a REIT | 90.00%rwt_MinimumPercentageOfTaxableIncomeDistributionToShareholders |  |
Minimum |  |  |
Significant Accounting Policies [Line Items] |  |  |
Incentive Plan, awards vesting period | 3 years |  |
Maximum |  |  |
Significant Accounting Policies [Line Items] |  |  |
Incentive Plan, awards vesting period | 4 years |  |

X
- Definition Employee Stock Purchase Plan, Minimum Percentage of Common Stock Fair Value Defined to Purchase Shares By Eligible Participants + References No definition available. + Details
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Namespace Prefix: | rwt_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Minimum Percentage of Taxable Income Distribution to Shareholders + References No definition available. + Details
Name: | rwt_MinimumPercentageOfTaxableIncomeDistributionToShareholders
Namespace Prefix: | rwt_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Share-Based Compensation Arrangement By Share-Based Payment Award, Award Holding Period + References No definition available. + Details
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Namespace Prefix: | rwt_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | rwt_SignificantAccountingPoliciesLineItems
Namespace Prefix: | rwt_
Data Type: | xbrli:stringItemType
Balance Type: | na
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- Definition Amount of discretionary contributions made by an employer to a defined contribution plan. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan. + References No definition available. + Details
Name: | us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
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- Details
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Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |