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	6 Months Ended	12 Months Ended
	Jun. 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	$ 43,098	$ 5,315
Expected weighted-average life (in years)	8 years	3 years
Prepayment speed assumption (annual CPR)	8.00%	33.00%
Decrease in fair value from:
10% adverse change	1,367	351
25% adverse change	3,284	812
Discount rate assumption	12.00%	12.00%
Decrease in fair value from:
100 basis point increase	1,822	121
200 basis point increase	3,309	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	123,591	10,409
Expected weighted-average life (in years)	6 years	3 years
Prepayment speed assumption (annual CPR)	13.00%	29.00%
Decrease in fair value from:
10% adverse change	4,275	724
25% adverse change	34,398	1,674
Discount rate assumption	5.00%	17.00%
Decrease in fair value from:
100 basis point increase	5,931	20
200 basis point increase	11,357	40
Credit loss assumption	0.22%	0.48%
Decrease in fair value from:
10% higher losses	39	5
25% higher losses	98	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	318,789	113,681
Expected weighted-average life (in years)	13 years	10 years
Prepayment speed assumption (annual CPR)	14.00%	24.00%
Decrease in fair value from:
10% adverse change	844	858
25% adverse change	1,974	1,909
Discount rate assumption	6.00%	6.00%
Decrease in fair value from:
100 basis point increase	28,365	901
200 basis point increase	52,835	1,791
Credit loss assumption	0.22%	0.47%
Decrease in fair value from:
10% higher losses	1,128	578
25% higher losses	$ 2,816	$ 1,446