SEGMENT REPORTING (Operating Segments and Reconciliation of Information to Condensed Consolidated Financial Statements) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Interest income	$ 87,214	$ 78,597	$ 175,397	$ 154,101
Interest expense	21,029	14,779	42,462	27,392
Provision (credit) for loan losses	1,633	1,733	1,505	3,730	$ 9,023
Non-interest income	16,556	14,868	33,525	31,986
Non-interest Expense	43,887	45,082	88,079	94,723
Income before income taxes	37,221	31,871	76,876	60,242
Income tax expense	8,945	7,472	18,283	14,178
Net income	28,276	24,399	58,593	46,064
Assets	8,398,519	8,152,600	8,398,519	8,152,600	$ 8,243,272
Intersegment Elimination
Segment Reporting Information [Line Items]
Interest income	(4)	(2)	(7)	(3)
Interest expense	(4)	(2)	(7)	(3)
Provision (credit) for loan losses	0	0	0	0
Non-interest income	(166)	(153)	(333)	(307)
Non-interest Expense	(166)	(153)	(333)	(307)
Income before income taxes	0	0	0	0
Income tax expense	0	0	0	0
Net income	0	0	0	0
Assets	(31,549)	(26,805)	(31,549)	(26,805)
Community Banking
Segment Reporting Information [Line Items]
Interest income	87,214	78,596	175,397	154,100
Interest expense	21,033	14,781	42,469	27,395
Provision (credit) for loan losses	1,633	1,733	1,505	3,730
Non-interest income	12,856	11,252	25,563	24,423
Non-interest Expense	40,859	42,302	82,070	89,333
Income before income taxes	36,545	31,032	74,916	58,065
Income tax expense	8,769	7,249	17,762	13,602
Net income	27,776	23,783	57,154	44,463
Assets	8,398,263	8,154,957	8,398,263	8,154,957
Insurance
Segment Reporting Information [Line Items]
Interest income	1	1	2	1
Interest expense	0	0	0	0
Provision (credit) for loan losses	0	0	0	0
Non-interest income	1,269	1,179	3,173	3,001
Non-interest Expense	1,304	1,302	2,724	2,681
Income before income taxes	(34)	(122)	451	321
Income tax expense	(8)	(32)	127	91
Net income	(26)	(90)	324	230
Assets	11,552	9,041	11,552	9,041
Investment Management
Segment Reporting Information [Line Items]
Interest income	3	2	5	3
Interest expense	0	0	0	0
Provision (credit) for loan losses	0	0	0	0
Non-interest income	2,597	2,590	5,122	4,869
Non-interest Expense	1,890	1,631	3,618	3,016
Income before income taxes	710	961	1,509	1,856
Income tax expense	184	255	394	485
Net income	526	706	1,115	1,371
Assets	$ 20,253	$ 15,407	$ 20,253	$ 15,407