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Basic and Diluted Earnings Per Common Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share Disclosure [Line Items]
Basic earnings per common share	$ 0.32us-gaap_EarningsPerShareBasic	$ 0.53us-gaap_EarningsPerShareBasic	$ 0.19us-gaap_EarningsPerShareBasic	$ 0.14us-gaap_EarningsPerShareBasic	$ 0.30us-gaap_EarningsPerShareBasic	$ 0.26us-gaap_EarningsPerShareBasic	$ 0.78us-gaap_EarningsPerShareBasic	$ 0.72us-gaap_EarningsPerShareBasic	$ 1.18us-gaap_EarningsPerShareBasic	$ 2.05us-gaap_EarningsPerShareBasic	$ 1.61us-gaap_EarningsPerShareBasic
Net income attributable to Redwood	$ 27,122us-gaap_NetIncomeLoss	$ 45,097us-gaap_NetIncomeLoss	$ 16,017us-gaap_NetIncomeLoss	$ 12,333us-gaap_NetIncomeLoss	$ 25,135us-gaap_NetIncomeLoss	$ 21,929us-gaap_NetIncomeLoss	$ 65,573us-gaap_NetIncomeLoss	$ 60,160us-gaap_NetIncomeLoss	$ 100,569us-gaap_NetIncomeLoss	$ 173,246us-gaap_NetIncomeLoss	$ 131,769us-gaap_NetIncomeLoss
Basic weighted average common shares outstanding									82,837,369	81,985,897	79,529,950
Net effect of dilutive equity awards									985,591
Net effect of assumed convertible notes conversion to common shares									11,825,450	9,751,946
Diluted weighted average common shares outstanding									85,098,579	93,694,924	80,673,682
Diluted Earnings Per Common Share	$ 0.31us-gaap_EarningsPerShareDiluted	$ 0.50us-gaap_EarningsPerShareDiluted	$ 0.18us-gaap_EarningsPerShareDiluted	$ 0.14us-gaap_EarningsPerShareDiluted	$ 0.29us-gaap_EarningsPerShareDiluted	$ 0.25us-gaap_EarningsPerShareDiluted	$ 0.71us-gaap_EarningsPerShareDiluted	$ 0.69us-gaap_EarningsPerShareDiluted	$ 1.15us-gaap_EarningsPerShareDiluted	$ 1.94us-gaap_EarningsPerShareDiluted	$ 1.59us-gaap_EarningsPerShareDiluted
Basic Earnings (Loss) Per Common Share
Earnings Per Share Disclosure [Line Items]
Net income attributable to Redwood									100,569	173,246	131,769
Less: Dividends and undistributed earnings allocated to participating securities									(2,612)	(4,899)	(3,886)
Net income allocated to common shareholders									97,957	168,347	127,883
Basic weighted average common shares outstanding									82,837,369	81,985,897	79,529,950
Diluted Earnings (Loss) Per Common Share
Earnings Per Share Disclosure [Line Items]
Net income attributable to Redwood									100,569	173,246	131,769
Less: Dividends and undistributed earnings allocated to participating securities									(2,524)	(3,726)	(3,212)
Add back: Interest expense on convertible notes										12,641
Net income allocated to common shareholders									$ 98,045	$ 182,161	$ 128,557
Basic weighted average common shares outstanding									82,837,369	81,985,897	79,529,950
Net effect of dilutive equity awards									2,261,210	1,957,081	1,143,732
Net effect of assumed convertible notes conversion to common shares										9,751,946
Diluted weighted average common shares outstanding									85,098,579	93,694,924	80,673,682