Note 4. Loans and Allowance for Loan Losses (Detail) - TDR Loan Modifications (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Residential real estate
Troubled Debt Restructurings	$ 11,514	$ 9,355
Interest Only Payments [Member] | Performing to Modified Terms [Member] | Commercial Real Estate Owner Occupied [Member]
Residential real estate
Troubled Debt Restructurings		674
Interest Only Payments [Member] | Performing to Modified Terms [Member] | Commercial and Industrial [Member]
Residential real estate
Troubled Debt Restructurings	2,939	334
Interest Only Payments [Member] | Performing to Modified Terms [Member] | Commercial Real Estate Nonowner Occupied [Member]
Residential real estate
Troubled Debt Restructurings		3,357
Interest Only Payments [Member] | Performing to Modified Terms [Member] | Residential Real Estate Loans [Member]
Residential real estate
Troubled Debt Restructurings	961
Interest Only Payments [Member] | Performing to Modified Terms [Member] | Construction [Member]
Residential real estate
Troubled Debt Restructurings		3,619
Interest Only Payments [Member] | Not Performing to Modified Terms [Member] | Commercial Real Estate Owner Occupied [Member]
Residential real estate
Troubled Debt Restructurings	252
Interest Only Payments [Member] | Not Performing to Modified Terms [Member] | Commercial and Industrial [Member]
Residential real estate
Troubled Debt Restructurings	674
Interest Only Payments [Member] | Not Performing to Modified Terms [Member] | Residential Real Estate Loans [Member]
Residential real estate
Troubled Debt Restructurings	959	283
Interest Only Payments [Member] | Not Performing to Modified Terms [Member] | Construction [Member]
Residential real estate
Troubled Debt Restructurings	395
Interest Only Payments [Member] | Commercial Real Estate Owner Occupied [Member]
Residential real estate
Troubled Debt Restructurings	252	674
Interest Only Payments [Member] | Commercial and Industrial [Member]
Residential real estate
Troubled Debt Restructurings	3,613	334
Interest Only Payments [Member] | Commercial Real Estate Nonowner Occupied [Member]
Residential real estate
Troubled Debt Restructurings		3,357
Interest Only Payments [Member] | Residential Real Estate Loans [Member]
Residential real estate
Troubled Debt Restructurings	1,920	283
Interest Only Payments [Member] | Construction [Member]
Residential real estate
Troubled Debt Restructurings	395	3,619
Rate Reduction [Member] | Performing to Modified Terms [Member] | Commercial Real Estate Owner Occupied [Member]
Residential real estate
Troubled Debt Restructurings	442
Rate Reduction [Member] | Performing to Modified Terms [Member] | Commercial and Industrial [Member]
Residential real estate
Troubled Debt Restructurings	420	449
Rate Reduction [Member] | Performing to Modified Terms [Member] | Residential Real Estate Loans [Member]
Residential real estate
Troubled Debt Restructurings		420
Rate Reduction [Member] | Commercial Real Estate Owner Occupied [Member]
Residential real estate
Troubled Debt Restructurings	442
Rate Reduction [Member] | Commercial and Industrial [Member]
Residential real estate
Troubled Debt Restructurings	420	449
Rate Reduction [Member] | Residential Real Estate Loans [Member]
Residential real estate
Troubled Debt Restructurings		420
Maturity Extension at Lower Stated Rate Than Market Rate [Member] | Performing to Modified Terms [Member] | Commercial Real Estate Owner Occupied [Member]
Residential real estate
Troubled Debt Restructurings		219
Maturity Extension at Lower Stated Rate Than Market Rate [Member] | Performing to Modified Terms [Member] | Commercial Real Estate Nonowner Occupied [Member]
Residential real estate
Troubled Debt Restructurings	206
Maturity Extension at Lower Stated Rate Than Market Rate [Member] | Commercial Real Estate Owner Occupied [Member]
Residential real estate
Troubled Debt Restructurings		219
Maturity Extension at Lower Stated Rate Than Market Rate [Member] | Commercial Real Estate Nonowner Occupied [Member]
Residential real estate
Troubled Debt Restructurings	206
Reduction of Principal and Interest Payments [Member] | Performing to Modified Terms [Member] | Commercial Real Estate Nonowner Occupied [Member]
Residential real estate
Troubled Debt Restructurings	4,266
Reduction of Principal and Interest Payments [Member] | Commercial Real Estate Nonowner Occupied [Member]
Residential real estate
Troubled Debt Restructurings	4,266
Performing to Modified Terms [Member]
Residential real estate
Troubled Debt Restructurings	9,234	9,072
Not Performing to Modified Terms [Member]
Residential real estate
Troubled Debt Restructurings	$ 2,280	$ 283