Loans - Summary of Troubled Debt Restructurings by Loan Class, Excluding Purchased Non-Covered and Covered Loans (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
Financing Receivable, Modifications [Line Items]
Troubled debt restructuring loans	$ 20,500,000	$ 20,900,000	$ 20,200,000
Excluding Purchased Non-Covered and Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructuring loans	17,261,000	17,214,000	17,024,000
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	88	72	64
Troubled debt restructuring loans	17,261,000	17,214,000	17,024,000
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	4	4	4
Troubled debt restructuring loans	257,000	515,000	521,000
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Construction and Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	11	8	8
Troubled debt restructuring loans	1,917,000	1,896,000	1,926,000
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Commercial and Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	21	17	16
Troubled debt restructuring loans	7,080,000	6,913,000	6,693,000
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	43	37	35
Troubled debt restructuring loans	7,973,000	7,818,000	7,871,000
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	9	6	1
Troubled debt restructuring loans	34,000	72,000	13,000
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	32	20	16
Troubled debt restructuring loans	3,227,000	3,683,000	3,150,000
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	4	3	3
Troubled debt restructuring loans	507,000	525,000	533,000
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Construction and Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	4	2	1
Troubled debt restructuring loans	196,000	32,000	29,000
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Commercial and Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	2	4	3
Troubled debt restructuring loans	1,672,000	2,273,000	1,858,000
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	10	8	7
Troubled debt restructuring loans	759,000	834,000	704,000
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	12	3	2
Troubled debt restructuring loans	$ 93,000	$ 19,000	$ 26,000