Credit Risk Profile Based on Payment Activity (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Consumer, Other	$ 16,576	[1]	$ 18,963	[1]
Consumer, Automobile	791	[1]	772	[1]
Residential real estate, Home equity	13,045	[1]	14,063	[1]
Residential real estate, 1-4 family	9,384	[1]	9,764	[1]
Performing
Financing Receivable, Recorded Investment [Line Items]
Consumer, Other	13,843	[1]	16,676	[1]
Consumer, Automobile	784	[1]	753	[1]
Residential real estate, Home equity	12,605	[1]	13,734	[1]
Residential real estate, 1-4 family	8,156	[1]	8,794	[1]
Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Consumer, Other	2,733	[1]	2,287	[1]
Consumer, Automobile	7	[1]	19	[1]
Residential real estate, Home equity	440	[1]	329	[1]
Residential real estate, 1-4 family	$ 1,228	[1]	$ 970	[1]

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