Condensed Financial Information - Parent Company Only - Condensed Statements of Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
INCOME
Other income	$ 1,234	$ 190	$ 2,141
EXPENSE
Noninterest expenses	126,756	111,167	104,534
Income taxes benefit	23,272	16,888	27,469
NET INCOME	70,672	63,401	52,580
Parent Company
INCOME
Dividends from subsidiaries	36,905	30,589	26,665
Other income	408	(125)	2,750
TOTAL INCOME	37,313	30,464	29,415
EXPENSE
Interest on subordinated debentures	5,983	5,141	5,091
Noninterest expenses	464	506	377
TOTAL EXPENSE	6,447	5,647	5,468
Income before benefit for income taxes	30,866	24,817	23,947
Income taxes benefit	(1,646)	(1,130)	(2,018)
Income before equity in undistributed income of subsidiaries	32,512	25,947	25,965
Equity in undistributed income of subsidiaries	38,160	37,454	26,615
NET INCOME	$ 70,672	$ 63,401	$ 52,580