Credit Risk Profile Based on Payment Activity (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Financing Receivable, Recorded Investment [Line Items]
Consumer, Other	$ 21,252	[1]	$ 22,296	[1]
Consumer, Automobile	821	[1]	943	[1]
Residential real estate, Home equity	14,436	[1]	14,590	[1]
Residential real estate, 1-4 family	10,889	[1]	12,338	[1]
Performing
Financing Receivable, Recorded Investment [Line Items]
Consumer, Other	18,380	[1]	19,760	[1]
Consumer, Automobile	782	[1]	878	[1]
Residential real estate, Home equity	14,080	[1]	14,282	[1]
Residential real estate, 1-4 family	9,718	[1]	11,118	[1]
Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Consumer, Other	2,872	[1]	2,536	[1]
Consumer, Automobile	39	[1]	65	[1]
Residential real estate, Home equity	356	[1]	308	[1]
Residential real estate, 1-4 family	$ 1,171	[1]	$ 1,220	[1]

[1] Credit quality indicators are reviewed and updated as applicable on an ongoing basis in accordance with credit policies.