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Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	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	$ 0.6us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount	$ 0.2us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount	$ 0.3us-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.

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X

- Definition

Minimum Percentage of Taxable Income Distribution to Shareholders

+ References

No definition available.

+ Details

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X

- Definition

Share-Based Compensation Arrangement By Share-Based Payment Award, Award Holding Period

+ References

No definition available.

+ Details

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Balance Type:	na
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X

- Details

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Balance Type:	na
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X

- 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

X

- Definition

Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan.

+ References

No definition available.

+ Details

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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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X

- Details

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X

- Details

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