Noninterest Income - Gains and Losses on Derivatives (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 exercises, net	$ 18,287	$ 7,449	$ 42,808	$ 22,482
Cancellations and expirations	(1,432)	(757)	(3,158)	(3,614)
Changes in fair value, net	17,286	18,230	32,743	23,564
Gains on equity warrant assets, net	$ 34,141	$ 24,922	$ 72,393	$ 42,432