Portion of Net Gains (Losses) Attributable to Level 3 Assets and Liabilities Still Held Included in Net Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Residential Loans at Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net gains (losses) attributable to level 3 assets still held included in net income	$ (1,864)	$ 11,662	$ (3,088)	$ 11,662
Commercial Loans at Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net gains (losses) attributable to level 3 assets still held included in net income	831	11	831	134
Trading Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net gains (losses) attributable to level 3 assets still held included in net income	(1,525)	28,937	28,491	71,136
Available-for-sale Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net gains (losses) attributable to level 3 assets still held included in net income		(1,207)	(940)	(1,842)
Derivative Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net gains (losses) attributable to level 3 liabilities still held included in net income		(2,304)		(3,394)
Mortgage Servicing Rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net gains (losses) attributable to level 3 assets still held included in net income	1,344	(578)	12,561	(1,029)
Asset-backed Securities | Acacia
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net gains (losses) attributable to level 3 liabilities still held included in net income		$ (28,167)		$ (73,193)