Loans - Summary of Troubled Debt Restructurings by Loan Class (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
Financing Receivable Modifications Number Of Contracts [Line Items]
Troubled debt restructuring loans	$ 20,500,000	$ 20,900,000	$ 20,200,000
Purchased Non-Covered Loans [Member]
Financing Receivable Modifications Number Of Contracts [Line Items]
Troubled debt restructuring loans	583,000	0
Purchased Non-Covered Loans [Member] | Accruing Loans [Member]
Financing Receivable Modifications Number Of Contracts [Line Items]
Number of contracts	6
Troubled debt restructuring loans	583,000
Purchased Non-Covered Loans [Member] | Accruing Loans [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable Modifications Number Of Contracts [Line Items]
Number of contracts	0
Troubled debt restructuring loans	0
Purchased Non-Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Construction and Development [Member]
Financing Receivable Modifications Number Of Contracts [Line Items]
Number of contracts	1
Troubled debt restructuring loans	305,000
Purchased Non-Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Commercial and Farmland [Member]
Financing Receivable Modifications Number Of Contracts [Line Items]
Number of contracts	0
Troubled debt restructuring loans	0
Purchased Non-Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Residential [Member]
Financing Receivable Modifications Number Of Contracts [Line Items]
Number of contracts	4
Troubled debt restructuring loans	275,000
Purchased Non-Covered Loans [Member] | Accruing Loans [Member] | Consumer Installment Loans [Member]
Financing Receivable Modifications Number Of Contracts [Line Items]
Number of contracts	1
Troubled debt restructuring loans	3,000
Purchased Non-Covered Loans [Member] | Non-Accruing Loans [Member]
Financing Receivable Modifications Number Of Contracts [Line Items]
Number of contracts	2
Troubled debt restructuring loans	247,000
Purchased Non-Covered Loans [Member] | Non-Accruing Loans [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable Modifications Number Of Contracts [Line Items]
Number of contracts	0
Troubled debt restructuring loans	0
Purchased Non-Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Construction and Development [Member]
Financing Receivable Modifications Number Of Contracts [Line Items]
Number of contracts	0
Troubled debt restructuring loans	0
Purchased Non-Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Commercial and Farmland [Member]
Financing Receivable Modifications Number Of Contracts [Line Items]
Number of contracts	0
Troubled debt restructuring loans	0
Purchased Non-Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Residential [Member]
Financing Receivable Modifications Number Of Contracts [Line Items]
Number of contracts	2
Troubled debt restructuring loans	247,000
Purchased Non-Covered Loans [Member] | Non-Accruing Loans [Member] | Consumer Installment Loans [Member]
Financing Receivable Modifications Number Of Contracts [Line Items]
Number of contracts	0
Troubled debt restructuring loans	$ 0