Derivative Financial Instruments - Summary of Derivative Activity and Related Impact on Consolidated Statements of Income (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Equity warrant assets
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Gain (Loss) on Derivatives	$ 17,508	$ 1,545
Derivatives designated as hedging instruments | Interest rate risks
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Gain (Loss) on Derivatives	0	553
Derivatives designated as hedging instruments | Interest rate risks | Interest expense—borrowings
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Gain (Loss) on Derivatives	0	554
Derivatives designated as hedging instruments | Interest rate risks | Other noninterest income
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Gain (Loss) on Derivatives	0	(1)
Derivatives not designated as hedging instruments | Foreign Exchange Contract
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Gain (Loss) on Derivatives	(586)	863
Derivatives not designated as hedging instruments | Foreign Exchange Contract | Other noninterest income
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Gain (Loss) on Derivatives	(3,512)	(3,245)
Derivatives not designated as hedging instruments | Foreign Exchange Contract | Other noninterest income
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Gain (Loss) on Derivatives	2,926	4,108
Derivatives not designated as hedging instruments | Other derivative instruments
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Gain (Loss) on Derivatives	539	465
Derivatives not designated as hedging instruments | Other derivative instruments | Other noninterest income
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Gain (Loss) on Derivatives	(7,114)	(2,289)
Derivatives not designated as hedging instruments | Other derivative instruments | Other noninterest income
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Gain (Loss) on Derivatives	7,653	2,754
Derivatives not designated as hedging instruments | Other derivative instruments | Other derivative contracts | Other noninterest income
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Gain (Loss) on Derivatives	431	(276)
Derivatives not designated as hedging instruments | Equity warrant assets | gains and losses on equity warrant assets [Domain]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Gain (Loss) on Derivatives	$ 19,191	$ 6,690