Condensed Financial Information - Parent Company Only - Condensed Statements of Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
INCOME
Other income	$ 2,182	$ 3,123	$ 1,769
EXPENSE
Noninterest expenses	111,167	104,534	99,917
Income taxes (benefit) provision	16,888	27,469	21,321
NET INCOME AVAILABLE TO COMMON SHAREHOLDERS	63,401	52,580	41,518
Parent Company
INCOME
Dividends from subsidiaries	30,589	26,665	20,687
Other income	(125)	2,750	199
TOTAL INCOME	30,464	29,415	20,886
EXPENSE
Interest on subordinated debentures	5,141	5,091	2,171
Noninterest expenses	506	377	442
TOTAL EXPENSE	5,647	5,468	2,613
Income before (benefit) provision for income taxes	24,817	23,947	18,273
Income taxes (benefit) provision	(1,130)	(2,018)	(845)
Income before equity in undistributed income of subsidiaries	25,947	25,965	19,118
Equity in undistributed income of subsidiaries	37,454	26,615	22,400
NET INCOME AVAILABLE TO COMMON SHAREHOLDERS	$ 63,401	$ 52,580	$ 41,518