PARENT COMPANY FINANCIAL INFORMATION - Statements of Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income:
Other income									$ 3,976	$ 4,768	$ 5,048
Expenses:
Total expenses	$ 11,964	$ 15,500	$ 13,413	$ 19,524	$ 19,807	$ 20,292	$ 21,029	$ 21,433	60,401	82,561	63,637
Income before income tax expense	74,889	58,934	(19,686)	10,287	37,071	38,914	37,221	39,655	124,424	152,861	132,688
Income tax expense (benefit)	18,227	14,292	(5,348)	300	8,614	9,531	8,945	9,338	27,471	36,428	31,824
Net income	$ 56,662	$ 44,642	$ (14,338)	$ 9,987	$ 28,457	$ 29,383	$ 28,276	$ 30,317	96,953	116,433	100,864
Parent Company
Income:
Cash dividends from subsidiary									74,410	42,625	39,370
Other income									932	1,093	897
Total income									75,342	43,718	40,267
Expenses:
Interest									9,028	3,141	1,922
Other expenses									1,505	1,507	1,135
Total expenses									10,533	4,648	3,057
Income before income tax expense									64,809	39,070	37,210
Income tax expense (benefit)									(1,988)	(734)	(283)
Income before equity in undistributed income of subsidiary									66,797	39,804	37,493
Equity in undistributed income of subsidiary									30,156	76,629	63,371
Net income									$ 96,953	$ 116,433	$ 100,864