SEGMENT REPORTING (Operating Segments and Reconciliation of Information to Condensed Consolidated Financial Statements) (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Interest income	$ 88,183	$ 75,504
Interest expense	21,433	12,613
Provision (credit) for loan losses	(128)	1,997	$ 9,023
Non-interest income	16,969	17,118
Non-interest Expense	44,192	49,641
Income before income taxes	39,655	28,371
Income tax expense	9,338	6,706
Net income	30,317	21,665
Assets	8,327,900	7,894,918	$ 8,243,272
Intersegment Elimination
Segment Reporting Information [Line Items]
Interest income	(3)	(1)
Interest expense	(3)	(1)
Provision (credit) for loan losses	0	0
Non-interest income	(167)	(154)
Non-interest Expense	(167)	(154)
Income before income taxes	0	0
Income tax expense	0	0
Net income	0	0
Assets	(30,324)	(25,246)
Community Banking
Segment Reporting Information [Line Items]
Interest income	88,183	75,504
Interest expense	21,436	12,614
Provision (credit) for loan losses	(128)	1,997
Non-interest income	12,707	13,171
Non-interest Expense	41,211	47,031
Income before income taxes	38,371	27,033
Income tax expense	8,993	6,353
Net income	29,378	20,680
Assets	8,326,141	7,894,964
Insurance
Segment Reporting Information [Line Items]
Interest income	1	0
Interest expense	0	0
Provision (credit) for loan losses	0	0
Non-interest income	1,904	1,822
Non-interest Expense	1,420	1,379
Income before income taxes	485	443
Income tax expense	135	123
Net income	350	320
Assets	11,519	8,984
Investment Management
Segment Reporting Information [Line Items]
Interest income	2	1
Interest expense	0	0
Provision (credit) for loan losses	0	0
Non-interest income	2,525	2,279
Non-interest Expense	1,728	1,385
Income before income taxes	799	895
Income tax expense	210	230
Net income	589	665
Assets	$ 20,564	$ 16,216