Loans and the Allowance for Credit Losses - Loans Identified as TDRs (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013 Contract	Sep. 30, 2012 Contract	Sep. 30, 2013 Contract	Sep. 30, 2012 Contract
Financing Receivable, Modifications [Line Items]
Number of Modifications	22	2	55	19
Pre-Modification Outstanding Recorded Investment	$ 609	$ 1,396	$ 3,512	$ 4,180
Post-Modification Outstanding Recorded Investment	552	1,240	3,193	3,611
Commercial Real Estate - Land and Construction [Member]
Financing Receivable, Modifications [Line Items]
Number of Modifications	1		2	1
Pre-Modification Outstanding Recorded Investment	66		366	516
Post-Modification Outstanding Recorded Investment	65		359	516
Commercial Real Estate - Improved Property [Member]
Financing Receivable, Modifications [Line Items]
Number of Modifications	1	1	6	9
Pre-Modification Outstanding Recorded Investment	49	1,073	568	2,741
Post-Modification Outstanding Recorded Investment	49	917	395	2,162
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Modifications	2	1	8	10
Pre-Modification Outstanding Recorded Investment	115	1,073	934	3,257
Post-Modification Outstanding Recorded Investment	114	917	754	2,678
Commercial and Industrial [Member]
Financing Receivable, Modifications [Line Items]
Number of Modifications	1		7	2
Pre-Modification Outstanding Recorded Investment	14		164	40
Post-Modification Outstanding Recorded Investment	14		161	37
Residential Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Modifications	8	1	24	7
Pre-Modification Outstanding Recorded Investment	307	323	2,180	883
Post-Modification Outstanding Recorded Investment	280	323	2,094	896
Home Equity [Member]
Financing Receivable, Modifications [Line Items]
Number of Modifications	2		3
Pre-Modification Outstanding Recorded Investment	75		91
Post-Modification Outstanding Recorded Investment	52		64
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Number of Modifications	9		13
Pre-Modification Outstanding Recorded Investment	98		143
Post-Modification Outstanding Recorded Investment	$ 92		$ 120