QUARTERLY FINANCIAL INFORMATION (Unaudited) (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 85,390	$ 87,082	$ 87,214	$ 88,183	$ 85,607	$ 84,374	$ 78,597	$ 75,504	$ 347,869	$ 324,082	$ 194,799
Interest expense	19,807	20,292	21,029	21,433	19,462	16,783	14,779	12,613	82,561	63,637	26,031
Net interest income	65,583	66,790	66,185	66,750	66,145	67,591	63,818	62,891	265,308	260,445	168,768
Provision (credit)	1,655	1,524	1,633	(128)	3,403	1,890	1,733	1,997	4,684	9,023	2,977
Non-interest income	19,224	18,573	16,556	16,969	14,030	15,033	14,868	17,118	71,322	61,049	51,243
Non-interest Expense	46,081	44,925	43,887	44,192	42,667	42,393	45,082	49,641	179,085	179,783	129,099
Income before income taxes	37,071	38,914	37,221	39,655	34,105	38,341	31,871	28,371	152,861	132,688	87,935
Income tax expense	8,614	9,531	8,945	9,338	8,539	9,107	7,472	6,706	36,428	31,824	34,726
Net income	$ 28,457	$ 29,383	$ 28,276	$ 30,317	$ 25,566	$ 29,234	$ 24,399	$ 21,665	$ 116,433	$ 100,864	$ 53,209
Earnings Per Share, Basic, Total	$ 0.80	$ 0.82	$ 0.79	$ 0.85	$ 0.72	$ 0.82	$ 0.68	$ 0.61	$ 3.25	$ 2.82	$ 2.20
Earnings Per Share, Diluted, Total	$ 0.80	$ 0.82	$ 0.79	$ 0.85	$ 0.72	$ 0.82	$ 0.68	$ 0.61	$ 3.25	$ 2.82	$ 2.20