Loans and the Allowance for Credit Losses - Loans Identified as TDRs (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013 Contract	Jun. 30, 2012 Contract	Jun. 30, 2013 Contract	Jun. 30, 2012 Contract
Schedule Of Financial Receivables [Line Items]
Number of Modifications	16	8	40	18
Pre-Modification Outstanding Recorded Investment	$ 842	$ 1,325	$ 3,441	$ 2,624
Post-Modification Outstanding Recorded Investment	840	1,333	3,191	2,638
Commercial Real Estate - Land and Construction [Member]
Schedule Of Financial Receivables [Line Items]
Number of Modifications		2	1	2
Pre-Modification Outstanding Recorded Investment		756	299	756
Post-Modification Outstanding Recorded Investment		756	295	756
Commercial Real Estate - Improved Property [Member]
Schedule Of Financial Receivables [Line Items]
Number of Modifications	3	2	8	8
Pre-Modification Outstanding Recorded Investment	120	364	1,011	1,268
Post-Modification Outstanding Recorded Investment	120	363	836	1,266
Commercial Real Estate [Member]
Schedule Of Financial Receivables [Line Items]
Number of Modifications	3	4	9	10
Pre-Modification Outstanding Recorded Investment	120	1,120	1,310	2,024
Post-Modification Outstanding Recorded Investment	120	1,119	1,131	2,022
Commercial and Industrial [Member]
Schedule Of Financial Receivables [Line Items]
Number of Modifications		2	6	2
Pre-Modification Outstanding Recorded Investment		39	161	40
Post-Modification Outstanding Recorded Investment		38	161	38
Residential Real Estate [Member]
Schedule Of Financial Receivables [Line Items]
Number of Modifications	9	2	16	6
Pre-Modification Outstanding Recorded Investment	673	166	1,883	560
Post-Modification Outstanding Recorded Investment	672	176	1,819	578
Home Equity [Member]
Schedule Of Financial Receivables [Line Items]
Number of Modifications	1		1
Pre-Modification Outstanding Recorded Investment	13		14
Post-Modification Outstanding Recorded Investment	13		13
Consumer [Member]
Schedule Of Financial Receivables [Line Items]
Number of Modifications	3		8
Pre-Modification Outstanding Recorded Investment	36		73
Post-Modification Outstanding Recorded Investment	$ 35		$ 67