Recorded Investment and Principal Balance of Impaired Loans by Portfolio Segment Their Related Allowance for Loan and Lease Losses and Interest Income Recognized (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012		Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Recorded Investment	$ 19,408	[1]	$ 21,637	[1]	$ 19,408	[1]	$ 21,637	[1]	$ 21,790	[2]
Principal Balance	20,950		22,142		20,950		22,142		22,563
Related Allowance	1,347		1,920		1,347		1,920		2,354
Average Principal Balance	21,327		24,166		21,275		24,132
Interest Income Recognized	110		97		210		299
Cash-Basis Interest Income Recognized
Impaired loans with related allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	7,660	[1]	9,413	[1]	7,660	[1]	9,413	[1]	11,967	[2]
Principal Balance	7,799		9,510		7,799		9,510		12,069
Related Allowance	1,347		1,920		1,347		1,920		2,354
Average Principal Balance	7,986		11,136		7,934		11,273
Interest Income Recognized	55		10		155		34
Cash-Basis Interest Income Recognized
Impaired loans with related allowance | Home equity lines and loans
Financing Receivable, Impaired [Line Items]
Recorded Investment	544	[1]	1,152	[1]	544	[1]	1,152	[1]	1,261	[2]
Principal Balance	589		1,210		589		1,210		1,321
Related Allowance	119		203		119		203		217
Average Principal Balance	619		1,211		617		1,211
Interest Income Recognized	5				15
Cash-Basis Interest Income Recognized
Impaired loans with related allowance | Residential mortgage
Financing Receivable, Impaired [Line Items]
Recorded Investment	4,448	[1]	1,708	[1]	4,448	[1]	1,708	[1]	4,778	[2]
Principal Balance	4,419		1,716		4,419		1,716		4,793
Related Allowance	628		229		628		229		667
Average Principal Balance	4,485		1,716		4,408		1,718
Interest Income Recognized	28		7		83		22
Cash-Basis Interest Income Recognized
Impaired loans with related allowance | Construction Loans
Financing Receivable, Impaired [Line Items]
Recorded Investment			3,678	[1]			3,678	[1]	2,564	[2]
Principal Balance			3,694				3,694		2,564
Related Allowance			698				698		543
Average Principal Balance			5,313				5,444
Cash-Basis Interest Income Recognized
Impaired loans with related allowance | Commercial and industrial
Financing Receivable, Impaired [Line Items]
Recorded Investment	2,586	[1]	2,856	[1]	2,586	[1]	2,856	[1]	3,357	[2]
Principal Balance	2,709		2,869		2,709		2,869		3,383
Related Allowance	544		771		544		771		919
Average Principal Balance	2,798		2,875		2,823		2,877
Interest Income Recognized	21		3		53		12
Cash-Basis Interest Income Recognized
Impaired loans with related allowance | Consumer
Financing Receivable, Impaired [Line Items]
Recorded Investment	82	[1]	19	[1]	82	[1]	19	[1]	7	[2]
Principal Balance	82		21		82		21		8
Related Allowance	56		19		56		19		8
Average Principal Balance	84		21		86		23
Interest Income Recognized	1				4
Cash-Basis Interest Income Recognized
Impaired loans without related allowance
Financing Receivable, Impaired [Line Items]
Recorded Investment	11,748	[1],[3],[4]	12,224	[1],[3],[5]	11,748	[1],[3],[4]	12,224	[1],[3],[5]	9,823	[2],[6]
Principal Balance	13,151	[3],[4]	12,632	[3],[5]	13,151	[3],[4]	12,632	[3],[5]	10,494	[6]
Average Principal Balance	13,341	[3],[4]	13,030	[3],[5]	13,341	[3],[4]	12,859	[3],[5]
Interest Income Recognized	55	[3],[4]	87	[3],[5]	55	[3],[4]	265	[3],[5]
Cash-Basis Interest Income Recognized		[3],[4]		[3],[5]		[3],[4]		[3],[5]
Impaired loans without related allowance | Commercial Mortgage
Financing Receivable, Impaired [Line Items]
Recorded Investment	421	[1],[3],[4]	343	[1],[3],[5]	421	[1],[3],[4]	343	[1],[3],[5]	541	[2],[6]
Principal Balance	432	[3],[4]	364	[3],[5]	432	[3],[4]	364	[3],[5]	574	[6]
Average Principal Balance	471	[3],[4]	364	[3],[5]	471	[3],[4]	364	[3],[5]
Interest Income Recognized							4	[3],[5]
Cash-Basis Interest Income Recognized		[3],[4]		[3],[5]		[3],[4]		[3],[5]
Impaired loans without related allowance | Home equity lines and loans
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,523	[1],[3],[4]	1,727	[1],[3],[5]	1,523	[1],[3],[4]	1,727	[1],[3],[5]	2,142	[2],[6]
Principal Balance	1,532	[3],[4]	1,795	[3],[5]	1,532	[3],[4]	1,795	[3],[5]	2,223	[6]
Average Principal Balance	1,631	[3],[4]	2,050	[3],[5]	1,631	[3],[4]	2,042	[3],[5]
Interest Income Recognized	2	[3],[4]	1	[3],[5]	2	[3],[4]	3	[3],[5]
Cash-Basis Interest Income Recognized		[3],[4]		[3],[5]		[3],[4]		[3],[5]
Impaired loans without related allowance | Residential mortgage
Financing Receivable, Impaired [Line Items]
Recorded Investment	5,091	[1],[3],[4]	7,992	[1],[3],[5]	5,091	[1],[3],[4]	7,992	[1],[3],[5]	4,433	[2],[6]
Principal Balance	5,340	[3],[4]	8,311	[3],[5]	5,340	[3],[4]	8,311	[3],[5]	4,741	[6]
Average Principal Balance	5,598	[3],[4]	8,324	[3],[5]	5,598	[3],[4]	8,231	[3],[5]
Interest Income Recognized	39	[3],[4]	68	[3],[5]	39	[3],[4]	204	[3],[5]
Cash-Basis Interest Income Recognized		[3],[4]		[3],[5]		[3],[4]		[3],[5]
Impaired loans without related allowance | Construction Loans
Financing Receivable, Impaired [Line Items]
Recorded Investment	3,072	[1],[3],[4]	1,317	[1],[3],[5]	3,072	[1],[3],[4]	1,317	[1],[3],[5]	2,067	[2],[6]
Principal Balance	4,035	[3],[4]	1,317	[3],[5]	4,035	[3],[4]	1,317	[3],[5]	2,317	[6]
Average Principal Balance	3,824	[3],[4]	1,446	[3],[5]	3,824	[3],[4]	1,376	[3],[5]
Interest Income Recognized	13	[3],[4]	15	[3],[5]	13	[3],[4]	44	[3],[5]
Cash-Basis Interest Income Recognized		[3],[4]		[3],[5]		[3],[4]		[3],[5]
Impaired loans without related allowance | Commercial and industrial
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,641	[1],[3],[4]	845	[1],[3],[5]	1,641	[1],[3],[4]	845	[1],[3],[5]	640	[2],[6]
Principal Balance	1,812	[3],[4]	845	[3],[5]	1,812	[3],[4]	845	[3],[5]	639	[6]
Average Principal Balance	1,817	[3],[4]	846	[3],[5]	1,817	[3],[4]	846	[3],[5]
Interest Income Recognized	1	[3],[4]	3	[3],[5]	1	[3],[4]	10	[3],[5]
Cash-Basis Interest Income Recognized		[3],[4]		[3],[5]		[3],[4]		[3],[5]

[1] Recorded investment equals principal balance less partial charge-offs and interest payments on non-performing loans that have been applied to principal.

[2] Recorded investment equals principal balance less partial charge-offs and interest payments on non-performing loans that have been applied to principal

[3] This table excludes all purchased credit-impaired loans, which are discussed in Note 5D, above.

[4] The table above does not include the recorded investment of $62 thousand of impaired leases without a related Allowance.

[5] The table above does not include the recorded investment of $223 thousand of impaired leases without a related allowance for loan and lease losses.

[6] The table above does not include the recorded investment of $168 thousand of impaired leases without a related Allowance.