Investment Securities - Schedule of Proceeds from Sales or Calls and Realized Gain and Losses of Available-for-sale Investment Securities and Other Securities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Proceeds from sales of available-for-sale debt securities	$ 424,140	$ 139,364	$ 342,233
Proceeds from calls of available-for-sale debt securities	1,175,272	419,270	438,818
Total	865,991	171,801	430,466
Realized gains on sales of available-for-sale debt securities	4,620	3,259	8,710
Realized losses on sales of available-for-sale debt securities	(2,760)	(1,469)	(263)
Other securities gains (losses)		50	667
Net debt securities gains (losses)	1,923	2,060	9,135
Calls [Member]
Debt Securities, Available-for-sale [Line Items]
Proceeds from calls of available-for-sale debt securities	441,851	32,437	88,233
Realized gains on calls of available-for-sale debt securities	93	283	29
Realized losses on calls of available-for-sale debt securities	$ (30)	$ (63)	$ (8)