Credit Risk Profile Based on Payment Activity (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Consumer, Other	$ 18,291	[1]	$ 18,963	[1]
Consumer, Automobile	698	[1]	772	[1]
Residential real estate, Home equity	13,436	[1]	14,063	[1]
Residential real estate, 1-4 family	9,432	[1]	9,764	[1]
Performing
Financing Receivable, Recorded Investment [Line Items]
Consumer, Other	14,208	[1]	16,676	[1]
Consumer, Automobile	687	[1]	753	[1]
Residential real estate, Home equity	12,768	[1]	13,734	[1]
Residential real estate, 1-4 family	7,780	[1]	8,794	[1]
Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Consumer, Other	4,083	[1]	2,287	[1]
Consumer, Automobile	11	[1]	19	[1]
Residential real estate, Home equity	668	[1]	329	[1]
Residential real estate, 1-4 family	$ 1,652	[1]	$ 970	[1]

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