Noninterest Income Summary of Other Noninterest Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Trading Activity, Gains and Losses, Net [Line Items]
Fund management fees	$ 21,214	$ 19,195	$ 15,941
Service-based fee income	3,860	7,962	8,767
Other	32,248	25,592	21,845
Other	59,110	50,750	47,004
Client Instruments [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Foreign Currency Transaction Gain (Loss), before Tax	10,882	4,215	115
Internal Instruments [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Foreign Currency Transaction Gain (Loss), before Tax	33,161	(16,676)	(12,735)
Derivatives not designated as hedging instruments | Client Instruments [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Unrealized Gain (Loss) on Derivatives	913	(1,459)	809
Other derivative instruments | Derivatives not designated as hedging instruments | Net gains on derivative instruments
Trading Activity, Gains and Losses, Net [Line Items]
Unrealized Gain (Loss) on Derivatives	(9,969)	(5,674)	694
Foreign Exchange Contract [Member] | Derivatives not designated as hedging instruments | Internal Instruments [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Unrealized Gain (Loss) on Derivatives	875	(540)	(358)
Foreign Exchange Contract [Member] | Derivatives not designated as hedging instruments | Net gains on derivative instruments
Trading Activity, Gains and Losses, Net [Line Items]
Unrealized Gain (Loss) on Derivatives	$ (32,286)	$ 16,136	$ 12,377