Loans and Allowance - Summary of Troubled Debt Restructurings by Modification (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Financing Receivable, Modifications [Line Items]
Modification	$ 11,955	$ 25,591
Troubled Debt Restructurings, Term Modifications
Financing Receivable, Modifications [Line Items]
Modification	7,452	20,412
Troubled Debt Restructurings, Rate Modifications
Financing Receivable, Modifications [Line Items]
Modification	1,290	1,178
Troubled Debt Restructurings, Rate and Term Modifications
Financing Receivable, Modifications [Line Items]
Modification	3,213	4,001
Commercial and industrial
Financing Receivable, Modifications [Line Items]
Modification	1,288	3,934
Commercial and industrial | Troubled Debt Restructurings, Term Modifications
Financing Receivable, Modifications [Line Items]
Modification	259	3,816
Commercial and industrial | Troubled Debt Restructurings, Rate and Term Modifications
Financing Receivable, Modifications [Line Items]
Modification	1,029	118
Construction
Financing Receivable, Modifications [Line Items]
Modification	625	723
Construction | Troubled Debt Restructurings, Term Modifications
Financing Receivable, Modifications [Line Items]
Modification		581
Construction | Troubled Debt Restructurings, Rate Modifications
Financing Receivable, Modifications [Line Items]
Modification		125
Construction | Troubled Debt Restructurings, Rate and Term Modifications
Financing Receivable, Modifications [Line Items]
Modification	625	17
Commercial and farm land
Financing Receivable, Modifications [Line Items]
Modification	7,952	14,102
Commercial and farm land | Troubled Debt Restructurings, Term Modifications
Financing Receivable, Modifications [Line Items]
Modification	6,668	10,338
Commercial and farm land | Troubled Debt Restructurings, Rate Modifications
Financing Receivable, Modifications [Line Items]
Modification	903	954
Commercial and farm land | Troubled Debt Restructurings, Rate and Term Modifications
Financing Receivable, Modifications [Line Items]
Modification	381	2,810
Residential
Financing Receivable, Modifications [Line Items]
Modification	1,900	6,731
Residential | Troubled Debt Restructurings, Term Modifications
Financing Receivable, Modifications [Line Items]
Modification	525	5,610
Residential | Troubled Debt Restructurings, Rate Modifications
Financing Receivable, Modifications [Line Items]
Modification	380	99
Residential | Troubled Debt Restructurings, Rate and Term Modifications
Financing Receivable, Modifications [Line Items]
Modification	995	1,022
Home Equity
Financing Receivable, Modifications [Line Items]
Modification		89
Home Equity | Troubled Debt Restructurings, Term Modifications
Financing Receivable, Modifications [Line Items]
Modification		55
Home Equity | Troubled Debt Restructurings, Rate and Term Modifications
Financing Receivable, Modifications [Line Items]
Modification		34
Consumer
Financing Receivable, Modifications [Line Items]
Modification	190
Consumer | Troubled Debt Restructurings, Rate Modifications
Financing Receivable, Modifications [Line Items]
Modification	7
Consumer | Troubled Debt Restructurings, Rate and Term Modifications
Financing Receivable, Modifications [Line Items]
Modification	183
Other Loans
Financing Receivable, Modifications [Line Items]
Modification		12
Other Loans | Troubled Debt Restructurings, Term Modifications
Financing Receivable, Modifications [Line Items]
Modification		$ 12