Noninterest Income - Gains and Losses on Derivatives (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]
Gains and Losses on Exercised Warrant Assets	$ 8,875	$ 3,121	$ 20,509	$ 11,345
Losses on Terminated Equity Warrant Assets	(826)	(571)	(1,726)	(1,129)
Unrealized Gain (Loss) on Derivatives	11,012	8,270	19,469	7,294
Gains on equity warrant assets, net	$ 19,061	$ 10,820	$ 38,252	$ 17,510