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, 2014 Contract	Jun. 30, 2013 Contract	Jun. 30, 2014 Contract	Jun. 30, 2013 Contract
Financing Receivable, Modifications [Line Items]
Number of Modifications	12	16	18	40
Pre-Modification Outstanding Recorded Investment	$ 282	$ 842	$ 530	$ 3,441
Post-Modification Outstanding Recorded Investment	275	840	509	3,191
Commercial Real Estate - Land and Construction [Member]
Financing Receivable, Modifications [Line Items]
Number of Modifications				1
Pre-Modification Outstanding Recorded Investment				299
Post-Modification Outstanding Recorded Investment				295
Commercial Real Estate - Improved Property [Member]
Financing Receivable, Modifications [Line Items]
Number of Modifications	1	3	2	8
Pre-Modification Outstanding Recorded Investment	112	120	203	1,011
Post-Modification Outstanding Recorded Investment	112	120	201	836
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Modifications	1	3	2	9
Pre-Modification Outstanding Recorded Investment	112	120	203	1,310
Post-Modification Outstanding Recorded Investment	112	120	201	1,131
Commercial and Industrial [Member]
Financing Receivable, Modifications [Line Items]
Number of Modifications				6
Pre-Modification Outstanding Recorded Investment				161
Post-Modification Outstanding Recorded Investment				161
Residential Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Modifications	2	9	5	16
Pre-Modification Outstanding Recorded Investment	70	673	189	1,883
Post-Modification Outstanding Recorded Investment	70	672	185	1,819
Home Equity [Member]
Financing Receivable, Modifications [Line Items]
Number of Modifications		1		1
Pre-Modification Outstanding Recorded Investment		13		14
Post-Modification Outstanding Recorded Investment		13		13
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Number of Modifications	9	3	11	8
Pre-Modification Outstanding Recorded Investment	100	36	138	73
Post-Modification Outstanding Recorded Investment	$ 93	$ 35	$ 123	$ 67