CREDIT QUALITY ASSESSMENT (Activity in Allowance for Loan and Lease Losses by Respective Loan Portfolio Segment) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year			$ 45,257	$ 44,067	$ 44,067
Provision (credit)	$ 1,890	$ 934	5,620	2,450	2,977
Charge-offs			(1,003)	(2,044)	(2,566)
Recoveries			535	451	779
Net charge-offs			(468)	(1,593)	(1,787)
Balance at period end	50,409	$ 44,924	50,409	44,924	45,257
Total loans and leases	$ 6,388,959		$ 6,388,959		$ 4,314,248
Allowance for loans and leases to total loans and leases ratio	0.79%		0.79%		1.05%
Balance of loans specifically evaluated for impairment	$ 18,348		$ 18,348		$ 20,809
Allowance for loans specifically evaluated for impairment	$ 4,204		$ 4,204		$ 4,014
Specific allowance to specific loans ratio	22.91%		22.91%		19.29%
Balance of loans collectively evaluated	$ 6,354,586		$ 6,354,586		$ 4,293,439
Allowance for loans collectively evaluated	46,205		$ 46,205		$ 41,243
Collective allowance to collective loans ratio			0.73%		0.96%
Financial Asset Acquired with Credit Deterioration [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance of loans acquired			$ 16,025
Allowance for loans acquired			$ 0
Allowance to loans acquired with deteriorated credity quality ratio			0.00%
Commercial
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year			$ 8,711	7,539	$ 7,539
Provision (credit)			1,472		2,616
Charge-offs			(437)		(1,538)
Recoveries			237		94
Net charge-offs			(200)		(1,444)
Balance at period end	9,983		9,983		8,711
Total loans and leases	$ 738,083		$ 738,083		$ 497,948
Allowance for loans and leases to total loans and leases ratio	1.35%		1.35%		1.75%
Balance of loans specifically evaluated for impairment	$ 7,123		$ 7,123		$ 8,105
Allowance for loans specifically evaluated for impairment	$ 2,827		$ 2,827		$ 3,220
Specific allowance to specific loans ratio	39.69%		39.69%		39.73%
Balance of loans collectively evaluated	$ 724,333		$ 724,333		$ 489,843
Allowance for loans collectively evaluated	7,156		$ 7,156		$ 5,491
Collective allowance to collective loans ratio			0.99%		1.12%
Commercial | Financial Asset Acquired with Credit Deterioration [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance of loans acquired			$ 6,627
Allowance for loans acquired			$ 0
Allowance to loans acquired with deteriorated credity quality ratio			0.00%
Consumer
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year			$ 2,383	2,828	$ 2,828
Provision (credit)			144		(57)
Charge-offs			(541)		(693)
Recoveries			113		305
Net charge-offs			(428)		(388)
Balance at period end	2,099		2,099		2,383
Total loans and leases	$ 523,011		$ 523,011		$ 455,829
Allowance for loans and leases to total loans and leases ratio	0.40%		0.40%		0.52%
Balance of loans collectively evaluated	$ 521,705		$ 521,705		$ 455,829
Allowance for loans collectively evaluated	2,099		$ 2,099		$ 2,383
Collective allowance to collective loans ratio			0.40%		0.52%
Consumer | Financial Asset Acquired with Credit Deterioration [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance of loans acquired			$ 1,306
Allowance for loans acquired			$ 0
Allowance to loans acquired with deteriorated credity quality ratio			0.00%
Commercial Real Estate Portfolio Segment | Commercial Acquisition, Development and Construction
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year			$ 3,501	4,652	$ 4,652
Provision (credit)			1,357		(1,254)
Charge-offs			0		0
Recoveries			62		103
Net charge-offs			62		103
Balance at period end	4,920		4,920		3,501
Total loans and leases	$ 631,589		$ 631,589		$ 292,443
Allowance for loans and leases to total loans and leases ratio	0.78%		0.78%		1.20%
Balance of loans specifically evaluated for impairment	$ 136		$ 136		$ 136
Allowance for loans specifically evaluated for impairment	$ 0		$ 0		$ 0
Specific allowance to specific loans ratio	0.00%		0.00%		0.00%
Balance of loans collectively evaluated	$ 631,453		$ 631,453		$ 292,307
Allowance for loans collectively evaluated	4,920		$ 4,920		$ 3,501
Collective allowance to collective loans ratio			0.78%		1.20%
Commercial Real Estate Portfolio Segment | Commercial Acquisition, Development and Construction | Financial Asset Acquired with Credit Deterioration [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance of loans acquired			$ 0
Allowance for loans acquired			$ 0
Allowance to loans acquired with deteriorated credity quality ratio			0.00%
Commercial Real Estate Portfolio Segment | Commercial Investor Real Estate
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year			$ 14,970	12,939	$ 12,939
Provision (credit)			2,145		1,930
Charge-offs			0		0
Recoveries			65		101
Net charge-offs			65		101
Balance at period end	17,180		17,180		14,970
Total loans and leases	$ 1,924,397		$ 1,924,397		$ 1,112,710
Allowance for loans and leases to total loans and leases ratio	0.89%		0.89%		1.35%
Balance of loans specifically evaluated for impairment	$ 5,861		$ 5,861		$ 5,575
Allowance for loans specifically evaluated for impairment	$ 1,255		$ 1,255		$ 663
Specific allowance to specific loans ratio	21.41%		21.41%		11.89%
Balance of loans collectively evaluated	$ 1,912,697		$ 1,912,697		$ 1,107,135
Allowance for loans collectively evaluated	15,925		$ 15,925		$ 14,307
Collective allowance to collective loans ratio			0.83%		1.29%
Commercial Real Estate Portfolio Segment | Commercial Investor Real Estate | Financial Asset Acquired with Credit Deterioration [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance of loans acquired			$ 5,839
Allowance for loans acquired			$ 0
Allowance to loans acquired with deteriorated credity quality ratio			0.00%
Commercial Real Estate Portfolio Segment | Commercial Owner Occupied Real Estate
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year			$ 7,178	7,885	$ 7,885
Provision (credit)			(577)		(459)
Charge-offs			0		(248)
Recoveries			0		0
Net charge-offs			0		(248)
Balance at period end	6,601		6,601		7,178
Total loans and leases	$ 1,201,673		$ 1,201,673		$ 857,196
Allowance for loans and leases to total loans and leases ratio	0.55%		0.55%		0.84%
Balance of loans specifically evaluated for impairment	$ 3,352		$ 3,352		$ 4,078
Allowance for loans specifically evaluated for impairment	$ 122		$ 122		$ 131
Specific allowance to specific loans ratio	3.64%		3.64%		3.21%
Balance of loans collectively evaluated	$ 1,196,079		$ 1,196,079		$ 853,118
Allowance for loans collectively evaluated	6,479		$ 6,479		$ 7,047
Collective allowance to collective loans ratio			0.54%		0.83%
Commercial Real Estate Portfolio Segment | Commercial Owner Occupied Real Estate | Financial Asset Acquired with Credit Deterioration [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance of loans acquired			$ 2,242
Allowance for loans acquired			$ 0
Allowance to loans acquired with deteriorated credity quality ratio			0.00%
Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year			$ 7,268	7,261	$ 7,261
Provision (credit)			892		(56)
Charge-offs			(25)		(87)
Recoveries			45		150
Net charge-offs			20		63
Balance at period end	8,180		8,180		7,268
Total loans and leases	$ 1,181,427		$ 1,181,427		$ 921,435
Allowance for loans and leases to total loans and leases ratio	0.69%		0.69%		0.79%
Balance of loans specifically evaluated for impairment	$ 1,876		$ 1,876		$ 2,915
Allowance for loans specifically evaluated for impairment	0		0		0
Balance of loans collectively evaluated	1,179,540		1,179,540		918,520
Allowance for loans collectively evaluated	8,180		$ 8,180		$ 7,268
Collective allowance to collective loans ratio			0.69%		0.79%
Residential Real Estate Portfolio Segment | Residential Mortgage | Financial Asset Acquired with Credit Deterioration [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance of loans acquired			$ 11
Allowance for loans acquired			$ 0
Allowance to loans acquired with deteriorated credity quality ratio			0.00%
Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year			$ 1,246	$ 963	$ 963
Provision (credit)			187		257
Charge-offs			0		0
Recoveries			13		26
Net charge-offs			13		26
Balance at period end	1,446		1,446		1,246
Total loans and leases	$ 188,779		$ 188,779		$ 176,687
Allowance for loans and leases to total loans and leases ratio	0.77%		0.77%		0.71%
Balance of loans specifically evaluated for impairment	$ 0		$ 0		$ 0
Allowance for loans specifically evaluated for impairment	0		0		0
Balance of loans collectively evaluated	188,779		188,779		176,687
Allowance for loans collectively evaluated	$ 1,446		$ 1,446		$ 1,246
Collective allowance to collective loans ratio			0.77%		0.71%
Residential Real Estate Portfolio Segment | Residential Construction | Financial Asset Acquired with Credit Deterioration [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance of loans acquired			$ 0
Allowance for loans acquired			$ 0
Allowance to loans acquired with deteriorated credity quality ratio			0.00%