Noninterest Income - Summary of Other Noninterest Income (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Trading Activity, Gains and Losses, Net [Line Items]
Fund management fees	$ 5,929	$ 5,536	$ 11,665	$ 10,705
Other	8,225	7,048	14,795	12,972
Other	14,390	12,811	26,649	25,232
Client Instruments
Trading Activity, Gains and Losses, Net [Line Items]
Foreign Currency Transaction Gain (Loss), before Tax	236	227	189	1,555
Other derivative instruments | Derivatives not designated as hedging instruments
Trading Activity, Gains and Losses, Net [Line Items]
Unrealized gains (losses) on derivatives	96	185	635	650
Foreign exchange contract | Derivatives not designated as hedging instruments
Trading Activity, Gains and Losses, Net [Line Items]
Unrealized gains (losses) on derivatives	$ 140	$ 42	$ (446)	$ 905