Loans - Summary of Trouble Debt Restructuring by Loan Class of 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
Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructuring loans	25,000,000	27,300,000	28,400,000
Covered Loans [Member] | Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	114	100	96
Troubled debt restructuring loans	22,757,000	22,243,000	20,981,000
Covered Loans [Member] | Accruing Loans [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	1	1
Troubled debt restructuring loans	26,000	13,000	12,000
Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Construction and Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3	3	5
Troubled debt restructuring loans	3,024,000	3,256,000	4,308,000
Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Commercial and Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	15	13	11
Troubled debt restructuring loans	8,501,000	7,255,000	6,200,000
Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	94	83	79
Troubled debt restructuring loans	11,202,000	11,719,000	10,461,000
Covered Loans [Member] | Accruing Loans [Member] | Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	0	0
Troubled debt restructuring loans	4,000	0	0
Covered Loans [Member] | Non-Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	23	24	26
Troubled debt restructuring loans	2,249,000	5,021,000	7,414,000
Covered Loans [Member] | Non-Accruing Loans [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	5	3
Troubled debt restructuring loans	3,000	71,000	40,000
Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Construction and Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3	4	4
Troubled debt restructuring loans	56,000	52,000	690,000
Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Commercial and Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	6	5	7
Troubled debt restructuring loans	1,225,000	3,946,000	4,805,000
Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	13	8	11
Troubled debt restructuring loans	965,000	942,000	1,874,000
Covered Loans [Member] | Non-Accruing Loans [Member] | Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	0	2	1
Troubled debt restructuring loans	$ 0	$ 10,000	$ 5,000