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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Interest income	$ 49,589	$ 42,857	$ 144,123	$ 126,313
Interest expense	6,892	5,126	18,847	15,728
Provision for loan losses	934	781	2,450	4,974	$ 5,546
Non-interest income	12,746	12,584	38,949	38,698
Non-interest Expense	31,191	29,326	94,040	92,514
Income before income taxes	23,318	20,208	67,735	51,795
Income tax expense	8,229	6,734	22,793	16,861
Net income	15,089	13,474	44,942	34,934
Assets	5,334,788	4,810,611	5,334,788	4,810,611	$ 5,091,383
Intersegment Elimination
Segment Reporting Information [Line Items]
Interest income	(3)	(2)	(7)	(6)
Interest expense	(3)	(2)	(7)	(6)
Provision for loan losses	0	0	0	0
Non-interest income	(209)	(179)	(628)	(535)
Non-interest Expense	(209)	(179)	(628)	(535)
Income before income taxes	0	0	0	0
Income tax expense	0	0	0	0
Net income	0	0	0	0
Assets	(18,057)	(21,387)	(18,057)	(21,387)
Community Banking
Segment Reporting Information [Line Items]
Interest income	49,590	42,856	144,123	126,313
Interest expense	6,895	5,128	18,854	15,734
Provision for loan losses	934	781	2,450	4,974
Non-interest income	8,915	9,071	28,545	29,426
Non-interest Expense	28,634	26,822	87,035	86,201
Income before income taxes	22,042	19,196	64,329	48,830
Income tax expense	7,725	6,339	21,454	15,701
Net income	14,317	12,857	42,875	33,129
Assets	5,333,539	4,811,948	5,333,539	4,811,948
Insurance
Segment Reporting Information [Line Items]
Interest income	0	1	1	2
Interest expense	0	0	0	0
Provision for loan losses	0	0	0	0
Non-interest income	1,948	1,783	4,923	4,186
Non-interest Expense	1,559	1,510	4,238	3,711
Income before income taxes	389	274	686	477
Income tax expense	158	108	279	191
Net income	231	166	407	286
Assets	7,499	7,986	7,499	7,986
Investment Management
Segment Reporting Information [Line Items]
Interest income	2	2	6	4
Interest expense	0	0	0	0
Provision for loan losses	0	0	0	0
Non-interest income	2,092	1,909	6,109	5,621
Non-interest Expense	1,207	1,173	3,395	3,137
Income before income taxes	887	738	2,720	2,488
Income tax expense	346	287	1,060	969
Net income	541	451	1,660	1,519
Assets	$ 11,807	$ 12,064	$ 11,807	$ 12,064