Summary of Derivative Activity and Related Impact on Consolidated Statements of Income (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
Derivatives designated as hedging instruments | Interest rate risks | Interest rate swaps | Interest expense-borrowings
Derivative Instruments, Gain (Loss) [Line Items]
Net gains (losses) on derivative instruments	$ 612		$ 2,337		$ 4,537		$ 12,205
Derivatives designated as hedging instruments | Interest rate risks | Interest rate swaps | Net gains on derivative instruments
Derivative Instruments, Gain (Loss) [Line Items]
Net gains (losses) on derivative instruments	74		(400)		571		(467)
Derivatives designated as hedging instruments | Interest rate risks | Interest Rate Risk
Derivative Instruments, Gain (Loss) [Line Items]
Net gains (losses) on derivative instruments	686		1,937		5,108		11,738
Derivatives not designated as hedging instruments | Currency exchange risks
Derivative Instruments, Gain (Loss) [Line Items]
Net gains (losses) on derivative instruments	1,798		(340)		1,258		(193)
Derivatives not designated as hedging instruments | Currency exchange risks | Loans | Other noninterest income
Derivative Instruments, Gain (Loss) [Line Items]
Net gains (losses) on derivative instruments	1,578		(3,931)		96		(733)
Derivatives not designated as hedging instruments | Currency exchange risks | Foreign exchange forwards | Net gains on derivative instruments
Derivative Instruments, Gain (Loss) [Line Items]
Net gains (losses) on derivative instruments	220		3,591		1,162		540
Derivatives not designated as hedging instruments | Other derivative instruments | Foreign exchange forwards | Net gains on derivative instruments
Derivative Instruments, Gain (Loss) [Line Items]
Net gains (losses) on derivative instruments	607		658		3,002		1,448
Derivatives not designated as hedging instruments | Other derivative instruments | Equity Warrant Asset | Net gains on derivative instruments
Derivative Instruments, Gain (Loss) [Line Items]
Net gains (losses) on derivative instruments	547		5,518		12,358		23,375
Derivatives not designated as hedging instruments | Other derivative instruments | Other derivatives | Net gains on derivative instruments
Derivative Instruments, Gain (Loss) [Line Items]
Net gains (losses) on derivative instruments	$ (337)	[1]	$ 584	[1]	$ (1,293)	[1]	$ (743)	[1]

[1] Primarily represents the change in fair value of loan conversion options.