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	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Proceeds from sales of investment securities available-for-sale	$ 20,028	$ 258,951	$ 256,438	$ 267,632
Proceeds from calls of available-for-sale debt securities	141,964	38,430	305,735	62,115
Total	161,992	297,381	562,173	329,747
Realized gains on sales of available-for-sale debt securities	545	3,032	6,140	3,103
Realized gains on calls of available-for-sale debt securities	27	0	40	3
Realized losses on sales of available-for-sale debt securities	(61)	(1,867)	(470)	(2,015)
Realized losses on calls of available-for-sale debt securities	0	0	(25)	(29)
Debt securities gains (losses), net	$ 511	$ 1,165	$ 5,685	$ 1,062