Loans and Allowance for Loan Losses - Summary of Troubled Debt Restructurings by Loan Class, Excluding Purchased Non-Covered and Covered Loans (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Modifications [Line Items]
Number of contracts	14	10
Troubled debt restructuring loans	$ 1,214	$ 3,390
Commercial, Financial & Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	3
Troubled debt restructuring loans	236	525
Real Estate - Construction & Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	1
Troubled debt restructuring loans	33	29
Commercial And Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	2	3
Troubled debt restructuring loans	570	2,197
Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	6	3
Troubled debt restructuring loans	314	639
Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	4
Troubled debt restructuring loans	61
Excluding Purchased Non-Covered and Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructuring loans	12,759	17,214	18,744
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	92	72
Troubled debt restructuring loans	12,759	17,214
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Commercial, Financial & Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	6	4
Troubled debt restructuring loans	290	515
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Construction & Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	9	8
Troubled debt restructuring loans	679	1,896
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Commercial And Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	19	17
Troubled debt restructuring loans	6,477	6,913
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	47	37
Troubled debt restructuring loans	5,258	7,818
Excluding Purchased Non-Covered and Covered Loans [Member] | Accruing Loans [Member] | Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	11	6
Troubled debt restructuring loans	55	72
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	32	20
Troubled debt restructuring loans	2,523	3,683
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Commercial, Financial & Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	2	3
Troubled debt restructuring loans	13	525
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Construction & Development [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	5	2
Troubled debt restructuring loans	228	32
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Commercial And Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3	4
Troubled debt restructuring loans	724	2,273
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Real Estate - Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	11	8
Troubled debt restructuring loans	1,485	834
Excluding Purchased Non-Covered and Covered Loans [Member] | Non-Accruing Loans [Member] | Consumer Installment Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	11	3
Troubled debt restructuring loans	$ 73	$ 19