Noninterest Income Summary of Other Noninterest Income (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Trading Activity, Gains and Losses, Net [Line Items]
Fund management fees	$ 5,736	$ 5,169
Other	6,570	5,924
Other	12,259	12,421
Client Instruments
Trading Activity, Gains and Losses, Net [Line Items]
Foreign Currency Transaction Gain (Loss), before Tax	(47)	1,328
Other derivative instruments | Derivatives not designated as hedging instruments
Trading Activity, Gains and Losses, Net [Line Items]
Unrealized Gain (Loss) on Derivatives	539	465
Other derivative instruments | Derivatives not designated as hedging instruments | Other noninterest income
Trading Activity, Gains and Losses, Net [Line Items]
Unrealized Gain (Loss) on Derivatives	(7,114)	(2,289)
Foreign Exchange Contract | Derivatives not designated as hedging instruments
Trading Activity, Gains and Losses, Net [Line Items]
Unrealized Gain (Loss) on Derivatives	(586)	863
Foreign Exchange Contract | Derivatives not designated as hedging instruments | Other noninterest income
Trading Activity, Gains and Losses, Net [Line Items]
Unrealized Gain (Loss) on Derivatives	$ (3,512)	$ (3,245)