Noninterest Income - Foreign Exchange Fees (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Gains and Losses on Derivatives [Abstract]
Brokerage Commissions Revenue	$ 31,548	$ 23,583	$ 62,750	$ 46,007
Forward Contract Commissions	2,455	2,470	4,940	6,071
Option Premium Fees	74	55	214	277
Foreign exchange fees	$ 34,077	$ 26,108	$ 67,904	$ 52,355