Aging of Recorded Investment in Loans by Class of Loans (Detail) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]    
30-59 Days Past Due $ 6,181 $ 7,443
60-89 Days Past Due 1,722 1,220
Over 90 Days Past Due 1,666 2,852
Total Past Due 9,569 11,515
Current 277,057 269,841
Recorded investment in loans 286,626 281,356
Residential
    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
30-59 Days Past Due 4,618 5,205
60-89 Days Past Due 1,377 1,068
Over 90 Days Past Due 1,122 1,035
Total Past Due 7,117 7,308
Current 104,988 109,560
Recorded investment in loans 112,105 116,868
Land
    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
30-59 Days Past Due 301 442
60-89 Days Past Due 4 43
Over 90 Days Past Due 0 43
Total Past Due 305 528
Current 9,402 9,444
Recorded investment in loans 9,707 9,972
Construction
    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
30-59 Days Past Due 113 0
60-89 Days Past Due 141 0
Over 90 Days Past Due 0 247
Total Past Due 254 247
Current 11,642 6,732
Recorded investment in loans 11,896 6,979
Commercial Real Estate
    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
30-59 Days Past Due 244 676
60-89 Days Past Due 0 0
Over 90 Days Past Due 443 1,258
Total Past Due 687 1,934
Current 63,419 55,906
Recorded investment in loans 64,106 57,840
Commercial Business
    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
30-59 Days Past Due 8 256
60-89 Days Past Due 17 0
Over 90 Days Past Due 0 0
Total Past Due 25 256
Current 19,167 20,520
Recorded investment in loans 19,192 20,776
Home Equity and Second Mortgage
    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
30-59 Days Past Due 584 558
60-89 Days Past Due 140 72
Over 90 Days Past Due 69 246
Total Past Due 793 876
Current 36,851 38,011
Recorded investment in loans 37,644 38,887
Other Consumer
    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
30-59 Days Past Due 313 306
60-89 Days Past Due 43 37
Over 90 Days Past Due 32 23
Total Past Due 388 366
Current 31,588 29,668
Recorded investment in loans $ 31,976 $ 30,034