PARENT COMPANY FINANCIAL INFORMATION (Statements of Income) (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income:
Other income									$ 4,916	$ 5,312	$ 5,521
Expenses:
Total interest expense	$ 7,184	$ 6,892	$ 6,250	$ 5,705	$ 5,276	$ 5,126	$ 5,071	$ 5,531	26,031	21,004	20,113
Income before income taxes and equity in undistributed income of of subsidiary	20,200	23,318	21,707	22,710	20,195	20,208	15,655	15,932	87,935	71,990	67,382
Income Tax Expense (Benefit)	(11,933)	(8,229)	(6,966)	(7,598)	(6,879)	(6,734)	(5,008)	(5,119)	(34,726)	(23,740)	(22,027)
Net income	$ 8,267	$ 15,089	$ 14,741	$ 15,112	$ 13,316	$ 13,474	$ 10,647	$ 10,813	53,209	48,250	45,355
Parent Company [Member]
Income:
Cash dividends from subsidiary									25,420	43,975	42,580
Other income									1,832	2,476	995
Total income									27,252	46,451	43,575
Expenses:
Interest									12	944	899
Other expenses									970	1,139	1,123
Total interest expense									982	2,083	2,022
Income before income taxes and equity in undistributed income of of subsidiary									26,270	44,368	41,553
Income Tax Expense (Benefit)									331	78	(308)
Income before equity in undistributed income of subsidiary									25,939	44,290	41,861
Equity in undistributed income of subsidiary									27,270	3,960	3,494
Net income									$ 53,209	$ 48,250	$ 45,355