Activity in Allowance for Loan and Lease Losses by Respective Loan Portfolio Segment (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	$ 49,426,000	$ 62,135,000	$ 64,559,000
Provision (credit)	3,649,000	1,428,000	25,908,000
Charge-offs	(12,804,000)	(16,505,000)
Loan and lease recoveries	2,686,000	2,368,000	4,284,000
Net charge-offs	(10,118,000)	(14,137,000)	(28,332,000)
Balance at period end	42,957,000	49,426,000	62,135,000
Total loans and leases	2,531,128,000	2,239,692,000
Allowance for loans and leases to total loans and leases ratio	1.70%	2.21%
Balance of loans specifically evaluated for impairment	48,773,000	67,575,000
Allowance for loans specifically evaluated for impairment	5,149,000	7,791,000	3,845,000
Specific loans to specific allowance ratio	10.56%	11.53%
Balance of loans collectively evaluated	2,482,355,000	2,172,117,000
Allowance for loans collectively evaluated	37,808,000	41,635,000	58,290,000
Collective loans to collective allowance ratio	1.52%	1.92%
Commercial Business
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	6,727,000	12,870,000
Provision (credit)	(758,000)	(4,252,000)
Charge-offs	(1,022,000)	(2,565,000)
Loan and lease recoveries	1,548,000	674,000
Net charge-offs	526,000	(1,891,000)
Balance at period end	6,495,000	6,727,000
Total loans and leases	346,708,000	260,327,000
Allowance for loans and leases to total loans and leases ratio	1.87%	2.58%
Balance of loans specifically evaluated for impairment	8,984,000	9,092,000
Allowance for loans specifically evaluated for impairment	2,597,000	1,037,000
Specific loans to specific allowance ratio	28.91%	11.41%
Balance of loans collectively evaluated	337,724,000	251,235,000
Allowance for loans collectively evaluated	3,898,000	5,690,000
Collective loans to collective allowance ratio	1.15%	2.26%
Leases
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	795,000	667,000
Provision (credit)	(478,000)	1,182,000
Charge-offs	(8,000)	(1,072,000)
Loan and lease recoveries	23,000	18,000
Net charge-offs	15,000	(1,054,000)
Balance at period end	332,000	795,000
Total loans and leases	3,421,000	6,954,000
Allowance for loans and leases to total loans and leases ratio	9.70%	11.43%
Balance of loans specifically evaluated for impairment	0
Allowance for loans specifically evaluated for impairment	0
Specific loans to specific allowance ratio	0.00%
Balance of loans collectively evaluated	3,421,000	6,954,000
Allowance for loans collectively evaluated	332,000	795,000
Collective loans to collective allowance ratio	9.70%	11.43%
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	4,873,000	4,231,000
Provision (credit)	44,000	3,173,000
Charge-offs	(1,298,000)	(2,740,000)
Loan and lease recoveries	227,000	209,000
Net charge-offs	(1,071,000)	(2,531,000)
Balance at period end	3,846,000	4,873,000
Total loans and leases	356,990,000	360,080,000
Allowance for loans and leases to total loans and leases ratio	1.08%	1.35%
Balance of loans specifically evaluated for impairment	31,000	35,000
Allowance for loans specifically evaluated for impairment	0
Specific loans to specific allowance ratio	0.00%
Balance of loans collectively evaluated	356,959,000	360,045,000
Allowance for loans collectively evaluated	3,846,000	4,873,000
Collective loans to collective allowance ratio	1.08%	1.35%
Commercial Real Estate Portfolio Segment | Commercial Acquisition, Development and Construction
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	6,664,000	18,241,000
Provision (credit)	826,000	(11,035,000)
Charge-offs	(3,281,000)	(1,780,000)
Loan and lease recoveries	528,000	1,238,000
Net charge-offs	(2,753,000)	(542,000)
Balance at period end	4,737,000	6,664,000
Total loans and leases	151,933,000	160,946,000
Allowance for loans and leases to total loans and leases ratio	3.12%	4.14%
Balance of loans specifically evaluated for impairment	6,332,000	18,701,000
Allowance for loans specifically evaluated for impairment	0	7,000
Specific loans to specific allowance ratio	0.00%	0.04%
Balance of loans collectively evaluated	145,601,000	142,245,000
Allowance for loans collectively evaluated	4,737,000	6,657,000
Collective loans to collective allowance ratio	3.25%	4.68%
Commercial Real Estate Portfolio Segment | Commercial Investor Real Estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	8,248,000	4,793,000
Provision (credit)	4,928,000	4,320,000
Charge-offs	(3,690,000)	(868,000)
Loan and lease recoveries	97,000	3,000
Net charge-offs	(3,593,000)	(865,000)
Balance at period end	9,583,000	8,248,000
Total loans and leases	456,888,000	371,948,000
Allowance for loans and leases to total loans and leases ratio	2.10%	2.22%
Balance of loans specifically evaluated for impairment	11,843,000	16,964,000
Allowance for loans specifically evaluated for impairment	774,000	3,380,000
Specific loans to specific allowance ratio	6.54%	19.92%
Balance of loans collectively evaluated	445,045,000	354,984,000
Allowance for loans collectively evaluated	8,809,000	4,868,000
Collective loans to collective allowance ratio	1.98%	1.37%
Commercial Real Estate Portfolio Segment | Commercial Owner Occupied Real Estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	7,329,000	8,177,000
Provision (credit)	804,000	(361,000)
Charge-offs	(1,174,000)	(487,000)
Loan and lease recoveries	38,000	0
Net charge-offs	(1,136,000)	(487,000)
Balance at period end	6,997,000	7,329,000
Total loans and leases	571,510,000	522,076,000
Allowance for loans and leases to total loans and leases ratio	1.22%	1.40%
Balance of loans specifically evaluated for impairment	15,184,000	15,416,000
Allowance for loans specifically evaluated for impairment	598,000	1,772,000
Specific loans to specific allowance ratio	3.94%	11.49%
Balance of loans collectively evaluated	556,326,000	506,660,000
Allowance for loans collectively evaluated	6,399,000	5,557,000
Collective loans to collective allowance ratio	1.15%	1.10%
Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	10,583,000	10,396,000
Provision (credit)	(167,000)	5,144,000
Charge-offs	(2,107,000)	(5,178,000)
Loan and lease recoveries	213,000	221,000
Net charge-offs	(1,894,000)	(4,957,000)
Balance at period end	8,522,000	10,583,000
Total loans and leases	523,364,000	448,662,000
Allowance for loans and leases to total loans and leases ratio	1.63%	2.36%
Balance of loans specifically evaluated for impairment	4,528,000	5,108,000
Allowance for loans specifically evaluated for impairment	713,000	769,000
Specific loans to specific allowance ratio	15.75%	15.05%
Balance of loans collectively evaluated	518,836,000	443,554,000
Allowance for loans collectively evaluated	7,809,000	9,814,000
Collective loans to collective allowance ratio	1.51%	2.21%
Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	4,207,000	2,760,000
Provision (credit)	(1,550,000)	3,257,000
Charge-offs	(224,000)	(1,815,000)
Loan and lease recoveries	12,000	5,000
Net charge-offs	(212,000)	(1,810,000)
Balance at period end	2,445,000	4,207,000
Total loans and leases	120,314,000	108,699,000
Allowance for loans and leases to total loans and leases ratio	2.03%	3.87%
Balance of loans specifically evaluated for impairment	1,871,000	2,259,000
Allowance for loans specifically evaluated for impairment	467,000	826,000
Specific loans to specific allowance ratio	24.96%	36.56%
Balance of loans collectively evaluated	118,443,000	106,440,000
Allowance for loans collectively evaluated	$ 1,978,000	$ 3,381,000
Collective loans to collective allowance ratio	1.67%	3.18%