Key Assumptions and Sensitivity Analysis for Assets Retained from Unconsolidated Variable Interest Entity's Sponsored by Redwood (Detail) (Variable Interest Entity, Not Primary Beneficiary, USD $) In Thousands, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2013		Dec. 31, 2012
Mortgage Servicing Rights
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Fair value	$ 56,244		$ 5,315
Expected life (in years)	8 years	[1]	3 years	[1]
Prepayment speed assumption (annual CPR)	9.00%	[1]	33.00%	[1]
Decrease in fair value from:
10% adverse change	1,905		351
25% adverse change	4,498		812
Discount rate assumption	11.00%	[1]	12.00%	[1]
Decrease in fair value from:
100 basis point increase	2,407		121
200 basis point increase	6,876		235
Interest-only Securities
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Fair value	117,443		10,409
Expected life (in years)	6 years	[1]	3 years	[1]
Prepayment speed assumption (annual CPR)	12.00%	[1]	29.00%	[1]
Decrease in fair value from:
10% adverse change	6,192		724
25% adverse change	31,332		1,674
Discount rate assumption	5.00%	[1]	17.00%	[1]
Decrease in fair value from:
100 basis point increase	5,668		20
200 basis point increase	10,851		40
Credit loss assumption	0.23%	[1]	0.48%	[1]
Decrease in fair value from:
10% higher losses	61		5
25% higher losses	154		12
Subordinate Securities
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Fair value	386,266		113,681
Expected life (in years)	13 years	[1]	10 years	[1]
Prepayment speed assumption (annual CPR)	13.00%	[1]	24.00%	[1]
Decrease in fair value from:
10% adverse change	930		858
25% adverse change	2,198		1,909
Discount rate assumption	6.00%	[1]	6.00%	[1]
Decrease in fair value from:
100 basis point increase	34,680		901
200 basis point increase	64,546		1,791
Credit loss assumption	0.23%	[1]	0.47%	[1]
Decrease in fair value from:
10% higher losses	1,268		578
25% higher losses	$ 3,169		$ 1,446

[1] Expected life, prepayment speed assumption, discount rate assumption, and credit loss assumption presented in the tables above represent weighted averages.