Condensed Financial Information - Parent Company Only - Condensed Statements of Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income
Other income (loss)	$ 735	$ 1,234	$ 190
Expense
Noninterest expenses	132,798	126,756	111,167
Income taxes benefit	17,259	23,272	16,888
Net Income	57,518	70,672	63,401
Parent Company
Income
Dividends from subsidiaries	29,961	36,905	30,589
Other income (loss)	(486)	408	(125)
Total Income	29,475	37,313	30,464
Expense
Interest on subordinated debentures	5,968	5,983	5,141
Noninterest expenses	549	464	506
Total Expense	6,517	6,447	5,647
Income before benefit for income taxes	22,958	30,866	24,817
Income taxes benefit	(1,645)	(1,646)	(1,130)
Income before equity in undistributed income of subsidiaries	24,603	32,512	25,947
Equity in undistributed income of subsidiaries	32,915	38,160	37,454
Net Income	$ 57,518	$ 70,672	$ 63,401