Summary of Troubled Debt Restructurings and Subsequent Defaults (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012
Financing Receivable, Modifications [Line Items]
Modification	$ 2,505	$ 6,695
Troubled Debt Restructurings, Term Modifications
Financing Receivable, Modifications [Line Items]
Modification		2,451
Troubled Debt Restructurings, Rate Modifications
Financing Receivable, Modifications [Line Items]
Modification	687	939
Troubled Debt Restructurings, Rate and Term Modifications
Financing Receivable, Modifications [Line Items]
Modification	1,818	3,305
Commercial and industrial
Financing Receivable, Modifications [Line Items]
Modification	1,048	1,302
Commercial and industrial | Troubled Debt Restructurings, Term Modifications
Financing Receivable, Modifications [Line Items]
Modification		230
Commercial and industrial | Troubled Debt Restructurings, Rate and Term Modifications
Financing Receivable, Modifications [Line Items]
Modification	1,048	1,072
Construction
Financing Receivable, Modifications [Line Items]
Modification	299	639
Construction | Troubled Debt Restructurings, Rate and Term Modifications
Financing Receivable, Modifications [Line Items]
Modification	299	639
Commercial and farm land
Financing Receivable, Modifications [Line Items]
Modification	875	2,758
Commercial and farm land | Troubled Debt Restructurings, Term Modifications
Financing Receivable, Modifications [Line Items]
Modification		1,693
Commercial and farm land | Troubled Debt Restructurings, Rate Modifications
Financing Receivable, Modifications [Line Items]
Modification	680	680
Commercial and farm land | Troubled Debt Restructurings, Rate and Term Modifications
Financing Receivable, Modifications [Line Items]
Modification	195	385
Residential
Financing Receivable, Modifications [Line Items]
Modification	167	1,880
Residential | Troubled Debt Restructurings, Term Modifications
Financing Receivable, Modifications [Line Items]
Modification		528
Residential | Troubled Debt Restructurings, Rate Modifications
Financing Receivable, Modifications [Line Items]
Modification		252
Residential | Troubled Debt Restructurings, Rate and Term Modifications
Financing Receivable, Modifications [Line Items]
Modification	167	1,100
Consumer
Financing Receivable, Modifications [Line Items]
Modification	116	116
Consumer | Troubled Debt Restructurings, Rate Modifications
Financing Receivable, Modifications [Line Items]
Modification	7	7
Consumer | Troubled Debt Restructurings, Rate and Term Modifications
Financing Receivable, Modifications [Line Items]
Modification	$ 109	$ 109