Activity in Allowance for Loan and Lease Losses by Respective Loan Portfolio Segment (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 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)	(2,798)		3,649
Charge-offs	(4,448)		(12,804)
Recoveries	3,304	933	2,686
Net charge-offs	(1,144)	(6,410)	(10,118)
Balance at period end	39,015	45,265	42,957
Total loans and leases	2,605,458		2,531,128
Allowance for loans and leases to total loans and leases ratio	1.50%		1.70%
Balance of loans specifically evaluated for impairment	38,809		48,773
Allowance for loans specifically evaluated for impairment	4,313		5,149
Specific allowance to specific loans ratio	11.11%		10.56%
Balance of loans collectively evaluated	2,566,649		2,482,355
Allowance for loans collectively evaluated	34,702		37,808
Collective allowance to collective loans ratio	1.35%		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)	1,529		(758)
Charge-offs	(2,243)		(1,022)
Recoveries	531		1,548
Net charge-offs	(1,712)		526
Balance at period end	6,312		6,495
Total loans and leases	334,979		346,708
Allowance for loans and leases to total loans and leases ratio	1.88%		1.87%
Balance of loans specifically evaluated for impairment	6,723		8,984
Allowance for loans specifically evaluated for impairment	1,397		2,597
Specific allowance to specific loans ratio	20.78%		28.91%
Balance of loans collectively evaluated	328,256		337,724
Allowance for loans collectively evaluated	4,915		3,898
Collective allowance to collective loans ratio	1.50%		1.15%
Leases
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	332	795	795
Provision (credit)	(303)		(478)
Charge-offs	0		(8)
Recoveries	4		23
Net charge-offs	4		15
Balance at period end	33		332
Total loans and leases	1,415		3,421
Allowance for loans and leases to total loans and leases ratio	2.33%		9.70%
Balance of loans collectively evaluated	1,415		3,421
Allowance for loans collectively evaluated	33		332
Collective allowance to collective loans ratio	2.33%		9.70%
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	3,846	4,873	4,873
Provision (credit)	939		44
Charge-offs	(1,083)		(1,298)
Recoveries	85		227
Net charge-offs	(998)		(1,071)
Balance at period end	3,787		3,846
Total loans and leases	363,114		356,990
Allowance for loans and leases to total loans and leases ratio	1.04%		1.08%
Balance of loans specifically evaluated for impairment	30		31
Balance of loans collectively evaluated	363,084		356,959
Allowance for loans collectively evaluated	3,787		3,846
Collective allowance to collective loans ratio	1.04%		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)	(3,441)		826
Charge-offs	0		(3,281)
Recoveries	2,464		528
Net charge-offs	2,464		(2,753)
Balance at period end	3,760		4,737
Total loans and leases	163,309		151,933
Allowance for loans and leases to total loans and leases ratio	2.30%		3.12%
Balance of loans specifically evaluated for impairment	5,885		6,332
Allowance for loans specifically evaluated for impairment	817		0
Specific allowance to specific loans ratio	13.88%		0.00%
Balance of loans collectively evaluated	157,424		145,601
Allowance for loans collectively evaluated	2,943		4,737
Collective allowance to collective loans ratio	1.87%		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)	(871)		4,928
Charge-offs	(276)		(3,690)
Recoveries	122		97
Net charge-offs	(154)		(3,593)
Balance at period end	8,558		9,583
Total loans and leases	497,365		456,888
Allowance for loans and leases to total loans and leases ratio	1.72%		2.10%
Balance of loans specifically evaluated for impairment	12,593		11,843
Allowance for loans specifically evaluated for impairment	167		774
Specific allowance to specific loans ratio	1.33%		6.54%
Balance of loans collectively evaluated	484,772		445,045
Allowance for loans collectively evaluated	8,391		8,809
Collective allowance to collective loans ratio	1.73%		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)	(47)		804
Charge-offs	(229)		(1,174)
Recoveries	48		38
Net charge-offs	(181)		(1,136)
Balance at period end	6,769		6,997
Total loans and leases	563,258		571,510
Allowance for loans and leases to total loans and leases ratio	1.20%		1.22%
Balance of loans specifically evaluated for impairment	7,009		15,184
Allowance for loans specifically evaluated for impairment	482		598
Specific allowance to specific loans ratio	6.88%		3.94%
Balance of loans collectively evaluated	556,249		556,326
Allowance for loans collectively evaluated	6,287		6,399
Collective allowance to collective loans ratio	1.13%		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)	(337)		(167)
Charge-offs	(513)		(2,107)
Recoveries	44		213
Net charge-offs	(469)		(1,894)
Balance at period end	7,716		8,522
Total loans and leases	565,282		523,364
Allowance for loans and leases to total loans and leases ratio	1.36%		1.63%
Balance of loans specifically evaluated for impairment	4,482		4,528
Allowance for loans specifically evaluated for impairment	684		713
Specific allowance to specific loans ratio	15.26%		15.75%
Balance of loans collectively evaluated	560,880		518,836
Allowance for loans collectively evaluated	7,032		7,809
Collective allowance to collective loans ratio	1.25%		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)	(267)		(1,550)
Charge-offs	(104)		(224)
Recoveries	6		12
Net charge-offs	(98)		(212)
Balance at period end	2,080		2,445
Total loans and leases	116,736		120,314
Allowance for loans and leases to total loans and leases ratio	1.78%		2.03%
Balance of loans specifically evaluated for impairment	2,087		1,871
Allowance for loans specifically evaluated for impairment	766		467
Specific allowance to specific loans ratio	36.70%		24.96%
Balance of loans collectively evaluated	114,649		118,443
Allowance for loans collectively evaluated	$ 1,314		$ 1,978
Collective allowance to collective loans ratio	1.15%		1.67%