Derivative Financial Instruments - Summary of Derivative Activity and Related Impact on Consolidated Statements of Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gain (loss) on derivatives	$ 20,404		$ (13,356)
Derivatives designated as hedging instruments | Interest rate risks | Interest rate swaps | Interest expense—borrowings
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gain (loss) on derivatives	638		639
Derivatives designated as hedging instruments | Interest rate risks | Interest rate swaps | Gain (Loss) on Derivative Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gain (loss) on derivatives	(3)		(12)
Derivatives designated as hedging instruments | Interest rate risks | Interest Rate Risk
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gain (loss) on derivatives	635		627
Derivatives not designated as hedging instruments | Currency exchange risks
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gain (loss) on derivatives	(141)		(51)
Derivatives not designated as hedging instruments | Currency exchange risks | Loans | Other noninterest income
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gain (loss) on derivatives	(20,159)		978
Derivatives not designated as hedging instruments | Currency exchange risks | Foreign exchange forwards | Gain (Loss) on Derivative Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gain (loss) on derivatives	20,018		(1,029)
Derivatives not designated as hedging instruments | Other derivative instruments | Foreign exchange forwards | Gain (Loss) on Derivative Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gain (loss) on derivatives	(507)		302
Derivatives not designated as hedging instruments | Other derivative instruments | Equity warrant assets | Gain (Loss) on Derivative Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gain (loss) on derivatives	20,278		25,373
Derivatives not designated as hedging instruments | Other derivative instruments | Other derivatives | Gain (Loss) on Derivative Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gain (loss) on derivatives	$ (57)	[1]	$ (467)	[1]

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