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, 2018	Mar. 31, 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)	1,997	194	2,977
Charge-offs	(477)	(482)	(2,566)
Recoveries	154	82	779
Net charge-offs	(323)	(400)	(1,787)
Balance at period end	46,931	43,861	45,257
Total loans and leases	$ 6,061,551		$ 4,314,248
Allowance for loans and leases to total loans and leases ratio	0.77%		1.05%
Balance of loans specifically evaluated for impairment	$ 20,793		$ 20,809
Allowance for loans specifically evaluated for impairment	$ 4,479		$ 4,014
Specific allowance to specific loans ratio	21.54%		19.29%
Balance of loans collectively evaluated	$ 6,040,758		$ 4,293,439
Allowance for loans collectively evaluated	$ 42,452		$ 41,243
Collective allowance to collective loans ratio	0.70%		0.96%
Commercial
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year	$ 8,711	7,539	$ 7,539
Provision (credit)	415		2,616
Charge-offs	(331)		(1,538)
Recoveries	9		94
Net charge-offs	(322)		(1,444)
Balance at period end	8,804		8,711
Total loans and leases	$ 652,797		$ 497,948
Allowance for loans and leases to total loans and leases ratio	1.35%		1.75%
Balance of loans specifically evaluated for impairment	$ 7,944		$ 8,105
Allowance for loans specifically evaluated for impairment	$ 3,096		$ 3,220
Specific allowance to specific loans ratio	38.97%		39.73%
Balance of loans collectively evaluated	$ 644,853		$ 489,843
Allowance for loans collectively evaluated	$ 5,708		$ 5,491
Collective allowance to collective loans ratio	0.89%		1.12%
Consumer
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year	$ 2,383	2,828	$ 2,828
Provision (credit)	226		(57)
Charge-offs	(146)		(693)
Recoveries	47		305
Net charge-offs	(99)		(388)
Balance at period end	2,510		2,383
Total loans and leases	$ 532,973		$ 455,829
Allowance for loans and leases to total loans and leases ratio	0.47%		0.52%
Balance of loans collectively evaluated	$ 532,973		$ 455,829
Allowance for loans collectively evaluated	$ 2,510		$ 2,383
Collective allowance to collective loans ratio	0.47%		0.52%
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)	254		(1,254)
Charge-offs	0		0
Recoveries	62		103
Net charge-offs	62		103
Balance at period end	3,817		3,501
Total loans and leases	$ 564,871		$ 292,443
Allowance for loans and leases to total loans and leases ratio	0.68%		1.20%
Balance of loans specifically evaluated for impairment	$ 136		$ 136
Allowance for loans specifically evaluated for impairment	$ 0		$ 0
Specific allowance to specific loans ratio	0.00%		0.00%
Balance of loans collectively evaluated	$ 564,735		$ 292,307
Allowance for loans collectively evaluated	$ 3,817		$ 3,501
Collective allowance to collective loans ratio	0.68%		1.20%
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)	1,102		1,930
Charge-offs	0		0
Recoveries	8		101
Net charge-offs	8		101
Balance at period end	16,080		14,970
Total loans and leases	$ 1,928,439		$ 1,112,710
Allowance for loans and leases to total loans and leases ratio	0.83%		1.35%
Balance of loans specifically evaluated for impairment	$ 5,813		$ 5,575
Allowance for loans specifically evaluated for impairment	$ 1,255		$ 663
Specific allowance to specific loans ratio	21.59%		11.89%
Balance of loans collectively evaluated	$ 1,922,626		$ 1,107,135
Allowance for loans collectively evaluated	$ 14,825		$ 14,307
Collective allowance to collective loans ratio	0.77%		1.29%
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)	(172)		(459)
Charge-offs	0		(248)
Recoveries	0		0
Net charge-offs	0		(248)
Balance at period end	7,006		7,178
Total loans and leases	$ 1,174,739		$ 857,196
Allowance for loans and leases to total loans and leases ratio	0.60%		0.84%
Balance of loans specifically evaluated for impairment	$ 4,009		$ 4,078
Allowance for loans specifically evaluated for impairment	$ 128		$ 131
Specific allowance to specific loans ratio	3.19%		3.21%
Balance of loans collectively evaluated	$ 1,170,730		$ 853,118
Allowance for loans collectively evaluated	$ 6,878		$ 7,047
Collective allowance to collective loans ratio	0.59%		0.83%
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)	(190)		(56)
Charge-offs	0		(87)
Recoveries	22		150
Net charge-offs	22		63
Balance at period end	7,100		7,268
Total loans and leases	$ 992,287		$ 921,435
Allowance for loans and leases to total loans and leases ratio	0.72%		0.79%
Balance of loans specifically evaluated for impairment	$ 2,891		$ 2,915
Allowance for loans specifically evaluated for impairment	0		0
Balance of loans collectively evaluated	989,396		918,520
Allowance for loans collectively evaluated	$ 7,100		$ 7,268
Collective allowance to collective loans ratio	0.72%		0.79%
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)	362		257
Charge-offs	0		0
Recoveries	6		26
Net charge-offs	6		26
Balance at period end	1,614		1,246
Total loans and leases	$ 215,445		$ 176,687
Allowance for loans and leases to total loans and leases ratio	0.75%		0.71%
Balance of loans specifically evaluated for impairment	$ 0		$ 0
Allowance for loans specifically evaluated for impairment	0		0
Balance of loans collectively evaluated	215,445		176,687
Allowance for loans collectively evaluated	$ 1,614		$ 1,246
Collective allowance to collective loans ratio	0.75%		0.71%