CREDIT QUALITY ASSESSMENT (Activity in Allowance for Loan and Lease Losses by Respective Loan Portfolio Segment) (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year				$ 44,067,000				$ 40,895,000	$ 44,067,000	$ 40,895,000	$ 37,802,000
Provision (credit)	$ 527,000	$ 934,000	$ 1,322,000	194,000	$ 572,000	$ 781,000	$ 2,957,000	1,236,000	2,977,000	5,546,000	5,371,000
Charge-offs									(2,566,000)	(3,134,000)	(3,795,000)
Recoveries									779,000	760,000	1,517,000
Net charge-offs									(1,787,000)	(2,374,000)	(2,278,000)
Balance at period end	45,257,000				44,067,000				45,257,000	44,067,000	40,895,000
Total loans and leases	$ 4,314,248,000				$ 3,927,808,000				$ 4,314,248,000	$ 3,927,808,000
Allowance for loans and leases to total loans and leases ratio	1.05%				1.12%				1.05%	1.12%
Balance of loans specifically evaluated for impairment	$ 20,809,000				$ 24,092,000				$ 20,809,000	$ 24,092,000
Allowance for loans specifically evaluated for impairment	$ 4,014,000				$ 4,825,000				$ 4,014,000	$ 4,825,000	3,375,000
Specific allowance to specific loans ratio	19.29%				20.03%				19.29%	20.03%
Balance of loans collectively evaluated	$ 4,293,439,000				$ 3,903,716,000				$ 4,293,439,000	$ 3,903,716,000
Allowance for loans collectively evaluated	41,243,000				39,242,000				$ 41,243,000	$ 39,242,000	37,520,000
Collective allowance to collective loans ratio									0.96%	1.01%
Commercial
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year				7,539,000				6,529,000	$ 7,539,000	$ 6,529,000
Provision (credit)									2,616,000	1,563,000
Charge-offs									(1,538,000)	(597,000)
Recoveries									94,000	44,000
Net charge-offs									(1,444,000)	(553,000)
Balance at period end	8,711,000				7,539,000				8,711,000	7,539,000	6,529,000
Total loans and leases	$ 497,948,000				$ 467,286,000				$ 497,948,000	$ 467,286,000
Allowance for loans and leases to total loans and leases ratio	1.75%				1.61%				1.75%	1.61%
Balance of loans specifically evaluated for impairment	$ 8,105,000				$ 7,018,000				$ 8,105,000	$ 7,018,000
Allowance for loans specifically evaluated for impairment	$ 3,220,000				$ 2,604,000				$ 3,220,000	$ 2,604,000
Specific allowance to specific loans ratio	39.73%				37.10%				39.73%	37.10%
Balance of loans collectively evaluated	$ 489,843,000				$ 460,268,000				$ 489,843,000	$ 460,268,000
Allowance for loans collectively evaluated	5,491,000				4,935,000				$ 5,491,000	$ 4,935,000
Collective allowance to collective loans ratio									1.12%	1.07%
Consumer
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year				2,828,000				3,456,000	$ 2,828,000	$ 3,456,000
Provision (credit)									(57,000)	112,000
Charge-offs									(693,000)	(888,000)
Recoveries									305,000	148,000
Net charge-offs									(388,000)	(740,000)
Balance at period end	2,383,000				2,828,000				2,383,000	2,828,000	3,456,000
Total loans and leases	$ 455,829,000				$ 456,657,000				$ 455,829,000	$ 456,657,000
Allowance for loans and leases to total loans and leases ratio	0.52%				0.62%				0.52%	0.62%
Balance of loans collectively evaluated	$ 455,829,000				$ 456,657,000				$ 455,829,000	$ 456,657,000
Allowance for loans collectively evaluated	2,383,000				2,828,000				$ 2,383,000	$ 2,828,000
Collective allowance to collective loans ratio									0.52%	0.62%
Commercial Real Estate Portfolio Segment | Commercial Acquisition, Development and Construction
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year				4,652,000				4,691,000	$ 4,652,000	$ 4,691,000
Provision (credit)									(1,254,000)	(31,000)
Charge-offs									0	(48,000)
Recoveries									103,000	40,000
Net charge-offs									103,000	(8,000)
Balance at period end	3,501,000				4,652,000				3,501,000	4,652,000	4,691,000
Total loans and leases	$ 292,443,000				$ 308,279,000				$ 292,443,000	$ 308,279,000
Allowance for loans and leases to total loans and leases ratio	1.20%				1.51%				1.20%	1.51%
Balance of loans specifically evaluated for impairment	$ 136,000				$ 137,000				$ 136,000	$ 137,000
Allowance for loans specifically evaluated for impairment	0				0				0	0
Balance of loans collectively evaluated	292,307,000				308,142,000				292,307,000	308,142,000
Allowance for loans collectively evaluated	3,501,000				4,652,000				$ 3,501,000	$ 4,652,000
Collective allowance to collective loans ratio									1.20%	1.51%
Commercial Real Estate Portfolio Segment | Commercial Investor Real Estate
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year				12,939,000				10,440,000	$ 12,939,000	$ 10,440,000
Provision (credit)									1,930,000	2,563,000
Charge-offs									0	(197,000)
Recoveries									101,000	133,000
Net charge-offs									101,000	(64,000)
Balance at period end	14,970,000				12,939,000				14,970,000	12,939,000	10,440,000
Total loans and leases	$ 1,112,710,000				$ 928,113,000				$ 1,112,710,000	$ 928,113,000
Allowance for loans and leases to total loans and leases ratio	1.35%				1.39%				1.35%	1.39%
Balance of loans specifically evaluated for impairment	$ 5,575,000				$ 8,107,000				$ 5,575,000	$ 8,107,000
Allowance for loans specifically evaluated for impairment	$ 663,000				$ 1,736,000				$ 663,000	$ 1,736,000
Specific allowance to specific loans ratio	11.89%				21.41%				11.89%	21.41%
Balance of loans collectively evaluated	$ 1,107,135,000				$ 920,006,000				$ 1,107,135,000	$ 920,006,000
Allowance for loans collectively evaluated	14,307,000				11,203,000				$ 14,307,000	$ 11,203,000
Collective allowance to collective loans ratio									1.29%	1.22%
Commercial Real Estate Portfolio Segment | Commercial Owner Occupied Real Estate
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year				7,885,000				7,984,000	$ 7,885,000	$ 7,984,000
Provision (credit)									(459,000)	(104,000)
Charge-offs									(248,000)	0
Recoveries									0	5,000
Net charge-offs									(248,000)	5,000
Balance at period end	7,178,000				7,885,000				7,178,000	7,885,000	7,984,000
Total loans and leases	$ 857,196,000				$ 775,552,000				$ 857,196,000	$ 775,552,000
Allowance for loans and leases to total loans and leases ratio	0.84%				1.02%				0.84%	1.02%
Balance of loans specifically evaluated for impairment	$ 4,078,000				$ 5,567,000				$ 4,078,000	$ 5,567,000
Allowance for loans specifically evaluated for impairment	$ 131,000				$ 485,000				$ 131,000	$ 485,000
Specific allowance to specific loans ratio	3.21%				8.71%				3.21%	8.71%
Balance of loans collectively evaluated	$ 853,118,000				$ 769,985,000				$ 853,118,000	$ 769,985,000
Allowance for loans collectively evaluated	7,047,000				7,400,000				$ 7,047,000	$ 7,400,000
Collective allowance to collective loans ratio									0.83%	0.96%
Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year				7,261,000				6,901,000	$ 7,261,000	$ 6,901,000
Provision (credit)									(56,000)	1,406,000
Charge-offs									(87,000)	(1,404,000)
Recoveries									150,000	358,000
Net charge-offs									63,000	(1,046,000)
Balance at period end	7,268,000				7,261,000				7,268,000	7,261,000	6,901,000
Total loans and leases	$ 921,435,000				$ 841,692,000				$ 921,435,000	$ 841,692,000
Allowance for loans and leases to total loans and leases ratio	0.79%				0.86%				0.79%	0.86%
Balance of loans specifically evaluated for impairment	$ 2,915,000				$ 3,263,000				$ 2,915,000	$ 3,263,000
Allowance for loans specifically evaluated for impairment	0				0				0	0
Balance of loans collectively evaluated	918,520,000				838,429,000				918,520,000	838,429,000
Allowance for loans collectively evaluated	7,268,000				7,261,000				$ 7,268,000	$ 7,261,000
Collective allowance to collective loans ratio									0.79%	0.87%
Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year				$ 963,000				$ 894,000	$ 963,000	$ 894,000
Provision (credit)									257,000	37,000
Charge-offs									0	0
Recoveries									26,000	32,000
Net charge-offs									26,000	32,000
Balance at period end	1,246,000				963,000				1,246,000	963,000	$ 894,000
Total loans and leases	$ 176,687,000				$ 150,229,000				$ 176,687,000	$ 150,229,000
Allowance for loans and leases to total loans and leases ratio	0.71%				0.64%				0.71%	0.64%
Balance of loans specifically evaluated for impairment	$ 0				$ 0				$ 0	$ 0
Allowance for loans specifically evaluated for impairment	0				0				0	0
Balance of loans collectively evaluated	176,687,000				150,229,000				176,687,000	150,229,000
Allowance for loans collectively evaluated	$ 1,246,000				$ 963,000				$ 1,246,000	$ 963,000
Collective allowance to collective loans ratio									0.71%	0.64%