CREDIT QUALITY ASSESSMENT (Activity in Allowance for Loan and Lease Losses by Respective Loan Portfolio Segment) (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year	$ 53,486	$ 45,257	$ 45,257
Provision (credit) for loan losses	(128)	1,997	9,023
Charge-offs	(356)	(477)	(1,416)
Recoveries	87	154	622
Net charge-offs	(269)	(323)	(794)
Balance at period end	53,089	46,931	53,486
Total loans and leases	$ 6,569,990		$ 6,571,634
Allowance for loans and leases to total loans and leases ratio	0.81%		0.81%
Balance of loans specifically evaluated for impairment	$ 26,140		$ 22,210
Allowance for loans specifically evaluated for impairment	$ 5,341		$ 4,924
Specific allowance to specific loans ratio	20.43%		22.17%
Balance of loans collectively evaluated	$ 6,524,288		$ 6,523,477
Allowance for loans collectively evaluated	$ 47,748		$ 48,562
Collective allowance to collective loans ratio	0.73%		0.74%
Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance of loans acquired	$ 19,562		$ 25,947
Allowance for loans acquired	0		0
Commercial
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year	11,377	8,711	8,711
Provision (credit) for loan losses	(422)		2,857
Charge-offs	(17)		(449)
Recoveries	10		258
Net charge-offs	(7)		(191)
Balance at period end	10,948		11,377
Total loans and leases	$ 769,660		$ 796,264
Allowance for loans and leases to total loans and leases ratio	1.42%		1.43%
Balance of loans specifically evaluated for impairment	$ 8,286		$ 7,586
Allowance for loans specifically evaluated for impairment	$ 3,624		$ 3,594
Specific allowance to specific loans ratio	43.74%		47.38%
Balance of loans collectively evaluated	$ 754,019		$ 780,523
Allowance for loans collectively evaluated	$ 7,324		$ 7,783
Collective allowance to collective loans ratio	0.97%		1.00%
Commercial | Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance of loans acquired	$ 7,355		$ 8,155
Allowance for loans acquired	0		0
Consumer
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year	2,113	2,383	2,383
Provision (credit) for loan losses	212		203
Charge-offs	(226)		(611)
Recoveries	44		138
Net charge-offs	(182)		(473)
Balance at period end	2,143		2,113
Total loans and leases	$ 505,443		$ 517,839
Allowance for loans and leases to total loans and leases ratio	0.42%		0.41%
Balance of loans collectively evaluated	$ 504,219		$ 516,567
Allowance for loans collectively evaluated	$ 2,143		$ 2,113
Collective allowance to collective loans ratio	0.43%		0.41%
Consumer | Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance of loans acquired	$ 1,224		$ 1,272
Allowance for loans acquired	0		0
Commercial Real Estate Portfolio Segment | Commercial Acquisition, Development and Construction
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year	5,944	3,501	3,501
Provision (credit) for loan losses	497		2,381
Charge-offs	0		0
Recoveries	0		62
Net charge-offs	0		62
Balance at period end	6,441		5,944
Total loans and leases	$ 688,939		$ 681,201
Allowance for loans and leases to total loans and leases ratio	0.93%		0.87%
Balance of loans specifically evaluated for impairment	$ 3,306		$ 3,306
Allowance for loans specifically evaluated for impairment	$ 151		$ 0
Specific allowance to specific loans ratio	0.00%		0.00%
Balance of loans collectively evaluated	$ 685,633		$ 677,895
Allowance for loans collectively evaluated	$ 6,290		$ 5,944
Collective allowance to collective loans ratio	0.92%		0.88%
Commercial Real Estate Portfolio Segment | Commercial Acquisition, Development and Construction | Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance of loans acquired	$ 0		$ 0
Allowance for loans acquired	0		0
Commercial Real Estate Portfolio Segment | Commercial Investor Real Estate
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year	17,603	14,970	14,970
Provision (credit) for loan losses	(329)		2,677
Charge-offs	0		(131)
Recoveries	7		87
Net charge-offs	7		(44)
Balance at period end	17,281		17,603
Total loans and leases	$ 1,962,879		$ 1,958,395
Allowance for loans and leases to total loans and leases ratio	0.88%		0.90%
Balance of loans specifically evaluated for impairment	$ 6,845		$ 5,355
Allowance for loans specifically evaluated for impairment	$ 1,315		$ 1,207
Specific allowance to specific loans ratio	19.21%		22.54%
Balance of loans collectively evaluated	$ 1,945,061		$ 1,938,712
Allowance for loans collectively evaluated	$ 15,966		$ 16,396
Collective allowance to collective loans ratio	0.82%		0.85%
Commercial Real Estate Portfolio Segment | Commercial Investor Real Estate | Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance of loans acquired	$ 10,973		$ 14,328
Allowance for loans acquired	0		0
Commercial Real Estate Portfolio Segment | Commercial Owner Occupied Real Estate
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year	6,307	7,178	7,178
Provision (credit) for loan losses	(139)		(871)
Charge-offs	0		0
Recoveries	0		0
Net charge-offs	0		0
Balance at period end	6,168		6,307
Total loans and leases	$ 1,216,713		$ 1,202,903
Allowance for loans and leases to total loans and leases ratio	0.51%		0.52%
Balance of loans specifically evaluated for impairment	$ 5,992		$ 4,234
Allowance for loans specifically evaluated for impairment	$ 251		$ 123
Specific allowance to specific loans ratio	4.19%		2.91%
Balance of loans collectively evaluated	$ 1,210,721		$ 1,196,487
Allowance for loans collectively evaluated	$ 5,917		$ 6,184
Collective allowance to collective loans ratio	0.49%		0.52%
Commercial Real Estate Portfolio Segment | Commercial Owner Occupied Real Estate | Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance of loans acquired	$ 0		$ 2,182
Allowance for loans acquired	0		0
Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year	8,881	7,268	7,268
Provision (credit) for loan losses	253		1,776
Charge-offs	(113)		(225)
Recoveries	24		62
Net charge-offs	(89)		(163)
Balance at period end	9,045		8,881
Total loans and leases	$ 1,249,968		$ 1,228,247
Allowance for loans and leases to total loans and leases ratio	0.72%		0.72%
Balance of loans specifically evaluated for impairment	$ 1,711		$ 1,729
Allowance for loans specifically evaluated for impairment	0		0
Balance of loans collectively evaluated	1,248,247		1,226,508
Allowance for loans collectively evaluated	$ 9,045		$ 8,881
Collective allowance to collective loans ratio	0.72%		0.72%
Residential Real Estate Portfolio Segment | Residential Mortgage | Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance of loans acquired	$ 10		$ 10
Allowance for loans acquired	0		0
Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year	1,261	$ 1,246	1,246
Provision (credit) for loan losses	(200)		0
Charge-offs	0		0
Recoveries	2		15
Net charge-offs	2		15
Balance at period end	1,063		1,261
Total loans and leases	$ 176,388		$ 186,785
Allowance for loans and leases to total loans and leases ratio	0.60%		0.68%
Balance of loans specifically evaluated for impairment	$ 0		$ 0
Allowance for loans specifically evaluated for impairment	0		0
Balance of loans collectively evaluated	176,388		186,785
Allowance for loans collectively evaluated	$ 1,063		$ 1,261
Collective allowance to collective loans ratio	0.60%		0.68%
Residential Real Estate Portfolio Segment | Residential Construction | Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance of loans acquired	$ 0		$ 0
Allowance for loans acquired	$ 0		$ 0