Credit Quality Assessment (Activity in Allowance for Loan and Lease Losses by Respective Loan Portfolio Segment) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year	$ 38,766,000	$ 42,957,000	$ 49,426,000
Provision (credit)	(163,000)	(1,084,000)
Charge-offs	(2,687,000)	(11,165,000)
Loan and lease recoveries	(1,886,000)	(8,058,000)	(2,686,000)
Net charge-offs	(801,000)	(3,107,000)	(10,118,000)
Balance at period end	37,802,000	38,766,000	42,957,000
Total loans and leases	3,127,392,000	2,784,266,000
Allowance for loans and leases to total loans and leases ratio	1.21%	1.39%
Balance of loans specifically evaluated for impairment	29,419,000	32,523,000
Allowance for loans specifically evaluated for impairment	2,894,000	3,058,000	5,149,000
Specific allowance to specific loans ratio	9.84%	9.40%
Balance of loans collectively evaluated	3,097,973,000	2,751,743,000
Allowance for loans collectively evaluated	34,908,000	35,708,000	37,808,000
Collective allowance to collective loans ratio	1.13%	1.30%
Commercial Business
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year	6,308,000	6,495,000
Provision (credit)	(1,204,000)	1,910,000
Charge-offs	(729,000)	(2,915,000)
Loan and lease recoveries	(1,477,000)	(818,000)
Net charge-offs	748,000	(2,097,000)
Balance at period end	5,852,000	6,308,000
Total loans and leases	390,781,000	356,651,000
Allowance for loans and leases to total loans and leases ratio	1.50%	1.77%
Balance of loans specifically evaluated for impairment	3,894,000	5,608,000
Allowance for loans specifically evaluated for impairment	788,000	849,000
Specific allowance to specific loans ratio	20.24%	15.14%
Balance of loans collectively evaluated	386,887,000	351,043,000
Allowance for loans collectively evaluated	5,064,000	5,459,000
Collective allowance to collective loans ratio	1.31%	1.56%
Leases
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year	16,000	332,000
Provision (credit)	(7,000)	(326,000)
Charge-offs	0	0
Loan and lease recoveries	0	(10,000)
Net charge-offs	0	10,000
Balance at period end	9,000	16,000
Total loans and leases	54,000	703,000
Allowance for loans and leases to total loans and leases ratio	16.80%	2.28%
Balance of loans collectively evaluated	54,000	703,000
Allowance for loans collectively evaluated	9,000	16,000
Collective allowance to collective loans ratio	16.80%	2.28%
Consumer
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year	4,142,000	3,846,000
Provision (credit)	119,000	1,951,000
Charge-offs	(834,000)	(1,853,000)
Loan and lease recoveries	(165,000)	(198,000)
Net charge-offs	(669,000)	(1,655,000)
Balance at period end	3,592,000	4,142,000
Total loans and leases	425,552,000	373,657,000
Allowance for loans and leases to total loans and leases ratio	0.84%	1.11%
Balance of loans specifically evaluated for impairment		29,000
Balance of loans collectively evaluated	425,552,000	373,628,000
Allowance for loans collectively evaluated	3,592,000	4,142,000
Collective allowance to collective loans ratio	0.84%	1.11%
Commercial Real Estate Portfolio Segment | Commercial Acquisition, Development and Construction
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year	3,754,000	4,737,000
Provision (credit)	1,042,000	(3,978,000)
Charge-offs	(529,000)	(85,000)
Loan and lease recoveries	0	(3,080,000)
Net charge-offs	(529,000)	2,995,000
Balance at period end	4,267,000	3,754,000
Total loans and leases	205,124,000	160,696,000
Allowance for loans and leases to total loans and leases ratio	2.08%	2.34%
Balance of loans specifically evaluated for impairment	2,464,000	4,128,000
Allowance for loans specifically evaluated for impairment	741,000	1,031,000
Specific allowance to specific loans ratio	30.07%	24.98%
Balance of loans collectively evaluated	202,660,000	156,568,000
Allowance for loans collectively evaluated	3,526,000	2,723,000
Collective allowance to collective loans ratio	1.74%	1.74%
Commercial Real Estate Portfolio Segment | Commercial Investor Real Estate
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year	9,263,000	9,583,000
Provision (credit)	486,000	1,100,000
Charge-offs	(3,000)	(4,774,000)
Loan and lease recoveries	(38,000)	(3,354,000)
Net charge-offs	35,000	(1,420,000)
Balance at period end	9,784,000	9,263,000
Total loans and leases	640,193,000	552,178,000
Allowance for loans and leases to total loans and leases ratio	1.53%	1.68%
Balance of loans specifically evaluated for impairment	10,279,000	7,654,000
Allowance for loans specifically evaluated for impairment	541,000	126,000
Specific allowance to specific loans ratio	5.26%	1.65%
Balance of loans collectively evaluated	629,914,000	544,524,000
Allowance for loans collectively evaluated	9,243,000	9,137,000
Collective allowance to collective loans ratio	1.47%	1.68%
Commercial Real Estate Portfolio Segment | Commercial Owner Occupied Real Estate
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year	6,308,000	6,997,000
Provision (credit)	1,094,000	(874,000)
Charge-offs	(265,000)	(240,000)
Loan and lease recoveries	(6,000)	(425,000)
Net charge-offs	(259,000)	185,000
Balance at period end	7,143,000	6,308,000
Total loans and leases	611,061,000	592,823,000
Allowance for loans and leases to total loans and leases ratio	1.17%	1.06%
Balance of loans specifically evaluated for impairment	8,941,000	7,111,000
Allowance for loans specifically evaluated for impairment	824,000	426,000
Specific allowance to specific loans ratio	9.22%	5.99%
Balance of loans collectively evaluated	602,120,000	585,712,000
Allowance for loans collectively evaluated	6,319,000	5,882,000
Collective allowance to collective loans ratio	1.05%	1.00%
Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year	7,819,000	8,522,000
Provision (credit)	(1,385,000)	329,000
Charge-offs	(323,000)	(1,194,000)
Loan and lease recoveries	(121,000)	(162,000)
Net charge-offs	(202,000)	(1,032,000)
Balance at period end	6,232,000	7,819,000
Total loans and leases	717,886,000	618,381,000
Allowance for loans and leases to total loans and leases ratio	0.87%	1.26%
Balance of loans specifically evaluated for impairment	3,535,000	6,141,000
Allowance for loans specifically evaluated for impairment	0	626,000
Specific allowance to specific loans ratio		10.19%
Balance of loans collectively evaluated	714,351,000	612,240,000
Allowance for loans collectively evaluated	6,232,000	7,193,000
Collective allowance to collective loans ratio	0.87%	1.17%
Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of year	1,156,000	2,445,000
Provision (credit)	(308,000)	(1,196,000)
Charge-offs	(4,000)	(104,000)
Loan and lease recoveries	(79,000)	(11,000)
Net charge-offs	75,000	(93,000)
Balance at period end	923,000	1,156,000
Total loans and leases	136,741,000	129,177,000
Allowance for loans and leases to total loans and leases ratio	0.67%	0.89%
Balance of loans specifically evaluated for impairment	306,000	1,852,000
Allowance for loans specifically evaluated for impairment	0	0
Balance of loans collectively evaluated	136,435,000	127,325,000
Allowance for loans collectively evaluated	$ 923,000	$ 1,156,000
Collective allowance to collective loans ratio	0.68%	0.91%