SEGMENT REPORTING (Operating Segments and Reconciliation of Information to Condensed Consolidated Financial Statements) (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Interest income	$ 44,243	$ 42,857	$ 41,803	$ 41,653	$ 41,074	$ 40,317	$ 38,849	$ 38,072	$ 170,556	$ 158,312	$ 148,366
Interest expense	5,276	5,126	5,071	5,531	5,297	5,201	4,916	4,699	21,004	20,113	18,818
Provision (credit)	572	781	2,957	1,236	1,850	1,706	1,218	597	5,546	5,371	(163)
Non-interest income	12,344	12,584	12,751	13,363	12,243	12,390	12,109	13,159	51,042	49,901	46,871
Non-interest Expense	30,544	29,326	30,871	32,317	26,996	29,630	29,477	29,244	123,058	115,347	120,800
Income before income taxes	20,195	20,208	15,655	15,932	19,174	16,170	15,347	16,691	71,990	67,382	55,782
Income tax expense	6,879	6,734	5,008	5,119	6,372	5,175	5,014	5,466	23,740	22,027	17,582
Net income	13,316	$ 13,474	$ 10,647	$ 10,813	12,802	$ 10,995	$ 10,333	$ 11,225	48,250	45,355	38,200
Assets	5,091,383				4,655,380				5,091,383	4,655,380	4,397,132
Intersegment Elimination
Segment Reporting Information [Line Items]
Interest income									(8)	(6)	(17)
Interest expense									(8)	(6)	(17)
Provision (credit)									0	0	0
Non-interest income									(713)	(16,117)	(3,701)
Non-interest Expense									(713)	(16,117)	(3,701)
Income before income taxes									0	0	0
Income tax expense									0	0	0
Net income									0	0	0
Assets	(22,282)				(19,393)				(22,282)	(19,393)	(19,756)
Community Banking
Segment Reporting Information [Line Items]
Interest income									170,556	158,313	148,366
Interest expense									21,012	20,119	18,835
Provision (credit)									5,546	5,371	(163)
Non-interest income									38,769	53,398	38,388
Non-interest Expense									114,368	122,183	115,577
Income before income taxes									68,399	64,038	52,505
Income tax expense									22,337	20,710	16,300
Net income									46,062	43,328	36,205
Assets	5,092,283				4,656,573				5,092,283	4,656,573	4,399,133
Insurance
Segment Reporting Information [Line Items]
Interest income									3	1	6
Interest expense									0	0	0
Provision (credit)									0	0	0
Non-interest income									5,418	5,516	5,386
Non-interest Expense									5,097	5,189	5,290
Income before income taxes									324	328	102
Income tax expense									130	141	43
Net income									194	187	59
Assets	7,732				5,542				7,732	5,542	5,842
Investment Management
Segment Reporting Information [Line Items]
Interest income									5	4	11
Interest expense									0	0	0
Provision (credit)									0	0	0
Non-interest income									7,568	7,104	6,798
Non-interest Expense									4,306	4,092	3,634
Income before income taxes									3,267	3,016	3,175
Income tax expense									1,273	1,176	1,239
Net income									1,994	1,840	1,936
Assets	$ 13,650				$ 12,658				$ 13,650	$ 12,658	$ 11,913