Schedule of Gains and Losses from Fair Value Changes (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Gains And Losses From Fair Value Changes [Line Items]
Gains (Losses) on Change in Fair Value	$ 20,364	$ 3,666	$ 26,742	$ 10,345
Net impairment losses on securities | Available for sale securities
Gains And Losses From Fair Value Changes [Line Items]
Gains (Losses) on Change in Fair Value	(4,697)		(5,247)	(825)
Trading Gains Net | Trading securities
Gains And Losses From Fair Value Changes [Line Items]
Gains (Losses) on Change in Fair Value	65	136	166	523
Trading Gains Net | Junior subordinated debentures issued to capital trusts
Gains And Losses From Fair Value Changes [Line Items]
Gains (Losses) on Change in Fair Value	(59)	640	461	2,587
Gains on Sales of Loans, Net | Loans held for sale
Gains And Losses From Fair Value Changes [Line Items]
Gains (Losses) on Change in Fair Value	$ 25,055	$ 2,890	$ 31,362	$ 8,060