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, 2020	Dec. 31, 2019	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Proceeds from sales of investment securities available-for-sale	$ 299,885	$ 424,140	$ 139,364
Proceeds from calls of available-for-sale debt securities	465,179	441,851	32,437
Total	765,064	865,991	171,801
Realized gains on sales of available-for-sale debt securities	11,172	4,620	3,259
Realized gains on calls of available-for-sale debt securities	121	93	283
Realized losses on sales of available-for-sale debt securities	(500)	(2,760)	(1,469)
Realized losses on calls of available-for-sale debt securities	(26)	(30)	(63)
Other securities gains (losses)	0	0	50
Debt securities gains (losses), net	$ 10,767	$ 1,923	$ 2,060