Noninterest Income - Summary of Noninterest Income (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other Income and Expenses [Abstract]
Gains on investment securities, net	$ 32,193	$ 15,238	$ 77,365	$ 48,838
Gains on equity warrant assets, net	34,141	24,922	72,393	42,432
Foreign exchange fees	32,656	29,671	100,560	82,026
Credit card fees	24,121	20,270	68,739	56,099
Deposit service charges	19,588	14,508	56,081	43,046
Client investment fees	36,265	15,563	88,592	37,571
Lending related fees	10,675	15,404	30,938	32,874
Letters of credit and standby letters of credit fees	8,409	7,306	24,938	20,951
Other	12,022	15,896	38,671	41,128
Total noninterest income	$ 210,070	$ 158,778	$ 558,277	$ 404,965