SEGMENT REPORTING (Operating Segments and Reconciliation of Information to Condensed Consolidated Financial Statements) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Interest income	$ 42,857	$ 40,317	$ 126,313	$ 117,238
Interest expense	5,126	5,201	15,728	14,816
Provision (credit)	781	1,706	4,974	3,521	$ 5,371
Non-interest income	12,584	12,390	38,698	37,658
Non-interest Expense	29,326	29,630	92,514	88,351
Income before income taxes	20,208	16,170	51,795	48,208
Income tax expense	6,734	5,175	16,861	15,655
Net income	13,474	10,995	34,934	32,553
Assets	4,810,611	4,611,034	4,810,611	4,611,034	$ 4,655,380
Intersegment Elimination
Segment Reporting Information [Line Items]
Interest income	(2)	(2)	(6)	(5)
Interest expense	(2)	(2)	(6)	(5)
Provision (credit)	0	0	0	0
Non-interest income	(179)	(181)	(535)	(15,936)
Non-interest Expense	(179)	(181)	(535)	(15,936)
Income before income taxes	0	0	0	0
Income tax expense	0	0	0	0
Net income	0	0	0	0
Assets	(21,387)	(18,302)	(21,387)	(18,302)
Community Banking
Segment Reporting Information [Line Items]
Interest income	42,856	40,318	126,313	117,238
Interest expense	5,128	5,203	15,734	14,821
Provision (credit)	781	1,706	4,974	3,521
Non-interest income	9,071	9,106	29,426	43,887
Non-interest Expense	26,822	27,318	86,201	97,294
Income before income taxes	19,196	15,197	48,830	45,489
Income tax expense	6,339	4,786	15,701	14,583
Net income	12,857	10,411	33,129	30,906
Assets	4,811,948	4,612,413	4,811,948	4,612,413
Insurance
Segment Reporting Information [Line Items]
Interest income	1	0	2	1
Interest expense	0	0	0	0
Provision (credit)	0	0	0	0
Non-interest income	1,783	1,716	4,186	4,394
Non-interest Expense	1,510	1,480	3,711	4,032
Income before income taxes	274	236	477	363
Income tax expense	108	101	191	153
Net income	166	135	286	210
Assets	7,986	5,788	7,986	5,788
Investment Management
Segment Reporting Information [Line Items]
Interest income	2	1	4	4
Interest expense	0	0	0	0
Provision (credit)	0	0	0	0
Non-interest income	1,909	1,749	5,621	5,313
Non-interest Expense	1,173	1,013	3,137	2,961
Income before income taxes	738	737	2,488	2,356
Income tax expense	287	288	969	919
Net income	451	449	1,519	1,437
Assets	$ 12,064	$ 11,135	$ 12,064	$ 11,135