Activity in Allowance for Loan and Lease Losses by Respective Loan Portfolio Segment (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	$ 42,957	$ 49,426	$ 49,426
Provision (credit)	(1,670)		3,649
Charge-offs	(9,639)		(12,804)
Loan and lease recoveries	7,774	2,167	2,686
Net charge-offs	(1,865)	(9,289)	(10,118)
Balance at period end	39,422	42,618	42,957
Total loans and leases	2,662,010		2,531,128
Allowance for loans and leases to total loans and leases ratio	1.48%		1.70%
Balance of loans specifically evaluated for impairment	31,089		48,773
Allowance for loans specifically evaluated for impairment	4,230		5,149
Specific allowance to specific loans ratio	13.61%		10.56%
Balance of loans collectively evaluated	2,630,921		2,482,355
Allowance for loans collectively evaluated	35,192		37,808
Collective allowance to collective loans ratio	1.34%		1.52%
Commercial Business
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	6,495	6,727	6,727
Provision (credit)	1,332		(758)
Charge-offs	(2,405)		(1,022)
Loan and lease recoveries	692		1,548
Net charge-offs	(1,713)		526
Balance at period end	6,114		6,495
Total loans and leases	332,670		346,708
Allowance for loans and leases to total loans and leases ratio	1.84%		1.87%
Balance of loans specifically evaluated for impairment	6,562		8,984
Allowance for loans specifically evaluated for impairment	1,550		2,597
Specific allowance to specific loans ratio	23.62%		28.91%
Balance of loans collectively evaluated	326,108		337,724
Allowance for loans collectively evaluated	4,564		3,898
Collective allowance to collective loans ratio	1.40%		1.15%
Leases
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	332	795	795
Provision (credit)	(321)		(478)
Charge-offs	0		(8)
Loan and lease recoveries	10		23
Net charge-offs	10		15
Balance at period end	21		332
Total loans and leases	962		3,421
Allowance for loans and leases to total loans and leases ratio	2.18%		9.70%
Balance of loans collectively evaluated	962		3,421
Allowance for loans collectively evaluated	21		332
Collective allowance to collective loans ratio	2.18%		9.70%
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	3,846	4,873	4,873
Provision (credit)	1,204		44
Charge-offs	(1,327)		(1,298)
Loan and lease recoveries	160		227
Net charge-offs	(1,167)		(1,071)
Balance at period end	3,883		3,846
Total loans and leases	368,764		356,990
Allowance for loans and leases to total loans and leases ratio	1.05%		1.08%
Balance of loans specifically evaluated for impairment	29		31
Balance of loans collectively evaluated	368,735		356,959
Allowance for loans collectively evaluated	3,883		3,846
Collective allowance to collective loans ratio	1.05%		1.08%
Commercial Real Estate Portfolio Segment | Commercial Acquisition, Development and Construction
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	4,737	6,664	6,664
Provision (credit)	(4,037)		826
Charge-offs	0		(3,281)
Loan and lease recoveries	3,080		528
Net charge-offs	3,080		(2,753)
Balance at period end	3,780		4,737
Total loans and leases	158,739		151,933
Allowance for loans and leases to total loans and leases ratio	2.38%		3.12%
Balance of loans specifically evaluated for impairment	5,086		6,332
Allowance for loans specifically evaluated for impairment	946		0
Specific allowance to specific loans ratio	18.60%		0.00%
Balance of loans collectively evaluated	153,653		145,601
Allowance for loans collectively evaluated	2,834		4,737
Collective allowance to collective loans ratio	1.84%		3.25%
Commercial Real Estate Portfolio Segment | Commercial Investor Real Estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	9,583	8,248	8,248
Provision (credit)	1,026		4,928
Charge-offs	(4,744)		(3,690)
Loan and lease recoveries	3,347		97
Net charge-offs	(1,397)		(3,593)
Balance at period end	9,212		9,583
Total loans and leases	518,029		456,888
Allowance for loans and leases to total loans and leases ratio	1.78%		2.10%
Balance of loans specifically evaluated for impairment	7,729		11,843
Allowance for loans specifically evaluated for impairment	146		774
Specific allowance to specific loans ratio	1.89%		6.54%
Balance of loans collectively evaluated	510,300		445,045
Allowance for loans collectively evaluated	9,066		8,809
Collective allowance to collective loans ratio	1.78%		1.98%
Commercial Real Estate Portfolio Segment | Commercial Owner Occupied Real Estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	6,997	7,329	7,329
Provision (credit)	(642)		804
Charge-offs	(229)		(1,174)
Loan and lease recoveries	332		38
Net charge-offs	103		(1,136)
Balance at period end	6,458		6,997
Total loans and leases	569,350		571,510
Allowance for loans and leases to total loans and leases ratio	1.13%		1.22%
Balance of loans specifically evaluated for impairment	5,385		15,184
Allowance for loans specifically evaluated for impairment	391		598
Specific allowance to specific loans ratio	7.26%		3.94%
Balance of loans collectively evaluated	563,965		556,326
Allowance for loans collectively evaluated	6,067		6,399
Collective allowance to collective loans ratio	1.08%		1.15%
Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	8,522	10,583	10,583
Provision (credit)	231		(167)
Charge-offs	(829)		(2,107)
Loan and lease recoveries	144		213
Net charge-offs	(685)		(1,894)
Balance at period end	8,068		8,522
Total loans and leases	595,180		523,364
Allowance for loans and leases to total loans and leases ratio	1.36%		1.63%
Balance of loans specifically evaluated for impairment	4,438		4,528
Allowance for loans specifically evaluated for impairment	650		713
Specific allowance to specific loans ratio	14.65%		15.75%
Balance of loans collectively evaluated	590,742		518,836
Allowance for loans collectively evaluated	7,418		7,809
Collective allowance to collective loans ratio	1.26%		1.51%
Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	2,445	4,207	4,207
Provision (credit)	(463)		(1,550)
Charge-offs	(105)		(224)
Loan and lease recoveries	9		12
Net charge-offs	(96)		(212)
Balance at period end	1,886		2,445
Total loans and leases	118,316		120,314
Allowance for loans and leases to total loans and leases ratio	1.59%		2.03%
Balance of loans specifically evaluated for impairment	1,860		1,871
Allowance for loans specifically evaluated for impairment	547		467
Specific allowance to specific loans ratio	29.41%		24.96%
Balance of loans collectively evaluated	116,456		118,443
Allowance for loans collectively evaluated	$ 1,339		$ 1,978
Collective allowance to collective loans ratio	1.15%		1.67%