Condensed Parent Company Financial Statements- Summary of Income Statement of Parent Company (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
OPERATING INCOME
Interest on interest-bearing deposits	$ 6,049	$ 31,368	$ 30,403
OPERATING EXPENSE
Other	43,859	44,829	39,887
Allocated income tax benefit	(23,926)	(34,683)	(33,938)
Amortization of stock-based compensation arrangements of subsidiaries	(1,516)	(1,277)	(1,352)
Net income	99,586	134,879	125,814
Parent Company [Member]
OPERATING INCOME
Dividends from subsidiaries	50,872	77,559	38,326
Interest on interest-bearing deposits	1	1,150	1,151
Other	886	451	16
Total operating income	51,759	79,160	39,493
OPERATING EXPENSE
Interest	1,965	1,965	2,172
Other	3,317	5,017	698
Total operating expense	5,282	6,982	2,870
Income before taxes	46,477	72,178	36,623
Allocated income tax benefit	2,610	2,731	3,093
Income before equity in undistributed earnings of subsidiaries	49,087	74,909	39,716
Equity in undistributed earnings of subsidiaries	51,955	61,194	87,404
Amortization of stock-based compensation arrangements of subsidiaries	(1,456)	(1,224)	(1,306)
Net income	$ 99,586	$ 134,879	$ 125,814